First, you need to decide if you want 3D printing to make things or you want 3D printers s as a hobby. If the former, I recommend at least $600 and preferably $1200 (Prusa Mk3 or Mk4, assembled) as an entry level machine.

That out of the way, there are a lot of kits out there which are fun to build, from models (Millennium Falcon or Rocinante) to sample ICE engines to fun and interesting mechanisms. If you get good with basic design you can print repairs and interesting things that are hard to buy. I’ve made weird stuff like a nut for a Toto flush handle, a customizable collet for pens in a Cricut machine, and a zero-stop for using the Warthog gaming throttle in a space flight sim. None of those are (or were) sold commercially when I designed them.

Printers are useful but ridiculously slow. A day for a single, 15 cm cubed part is not unusual. It’s a lot like building your own Slackware server. There are pre-built versions (unRaid) and a million uses - but if you don’t have one of those uses and aren’t willing to get your hands dirty and your head deep into forums to set things up and/or fix them, it will be a waste of time and money.

3D printing has many appeals, so it depends on you. May I ask how you came to the question of buying a printer? The "how" should give us some indication as to what could interest you.

I think its cheaper and easier to pay for 3D printing service to see what can you expect from the quality. But if you want to print mechanical parts that are not available online you have to learn 3D modeling.

Both worlds 3D printing and 3D modeling are huge hobbies and I love them, but its not for everyone. You need patience for both and lot of learning/tuning to achieve what you want. Failed print is quite normal for begginers and it is painfull!

Maybe consider CAD modeling sofware for mechanical parts (like solidworks) and make your first model, then you can pay for printing service (kinda cheap nowdays) and decide if that is for you.

The main reason I have 3D printer is because Im geek and I love thinkering. Parts I print would be much cheaper if I payed for printing service, but I dont regret. Having printer at my home and knowledge to model what I want makes me feel super powerful lol

I was thinking about automating some little things around the house with 3D printed mechanisms and raspberry pis, such as opening the blinds automatically at a certain time. I would have to design and 3d print the mechanism to make it work. Just an idea.

"is it worth it" questions are really tough to answer. For everyone, the internal calculus that makes it worth it is going to be different- and pretty arcane at that.

I honestly suspect that, if there's only one project (the engine), that you're going to finish- or not even start, after having learned the basic lessons (and there's a lot of lessons to learn. And keep learning... new materials all the time, with new properties new gadgets.)

If the motivation is to 'learn 3d printing' ... it's probably going to be something that stalls out. Which, if it's something you keep coming a back to.. that's okay. I would HIGHLY recommend looking into your local libraries, or for a local hackspace. many- probably most- public library networks will have at least one available for use. They may even offer classes.

just be sure to learn the limits of what can be printed... and what can't... feel free to ask.

I second comment from overzeetop's comment about prusa being entry level. you can make a creality machine print as good... but then it's no longer a creality machine. The prebuilt prusas from their shop is an amazing starter printer. and with some work and a lot of practice... will likely be capable of meeting demands in PLA, PETG, ASA, TPU, and with modifications all but the most troublesome of specialty filaments. (also the prusa community is wonderful. just saying.)

I use my printer as part of larger projects. Furniture gets new legs. Kitchen gets new spice rack. Appliances get small repairs or mods. TV gets soundbar attached. Desk gets hook for headphones. That kind of stuff. It's all one-of-a-kind and of no use to anybody else, but extremely satisfying to model, print, and use.

(I had a bunch of photos on Twitter. Can't link now, might copy to the Fediverse later.)

3D-printing isn't for everyone. However, most of us that got hooked have found ourselves spending 3-4 hours designing a spare part for a broken plastic thing that would have cost us $1 if we bought it.

It's more the trip than the destination for a lot of us. It's creation. It's art.

Some silly things I have downloaded / designed and printed:

• wall mount for a ZigBee motion detector
• detachable shelf for the dredge door
• gardena male connector prototype (going to design a sprayer for our mini greenhouse)
• vacuum cleaner pipe adapter (old attachments to new vacuum)
• Taylor made boxes for RPi and Arduino
• foldable dice tower
• astronaut token tningy for Planet Nine card game
• Custom made box for Exploding Kittens card game
• some cute Groot thing my SO wanted
• modifications for my 3D-printwr

There are numerous sites that may or may not give you inspiration.

https://www.printables.com

https://www.myminifactory.com

https://www.cults3d.com

Why not search for your bike / car model on https://www.yeggi.com ?

I'm still a rookie but here are my five cents regarding cogs mechanics: I'm not sure PLA is a good choice for things you put torque on. Normally Nylon is used and according to what I have understood that's no fun printing. PLA is the easiest. Next Step would be to try PETG. Then there is ABS and ASA which require more from you for a successful print but the reward is a result with a better durability. (Depending on application of course) Also there are toxic fumes when printing those so be careful. Google the different types of plastics and characteristics to get feeling for what to choose for what application.

Good luck.