I haven't built the OAT but I have built the larger variant (OpenAstroMount). OAM is pretty well designed in my opinion, with the biggest weak point being the connection to the tripod. In my case I machined a replacement for the printed part.
I believe OAT should be more than enough for light setup, but you have to make sure you have a good place to set it up. It isn't designed to sit on a tripod. They have a new model in the works (OpenAstroExplorer) which I believe is designed for tripod use without being as massive as the OAM.
You can bring the cost down by purchasing components for cheap on AliExpress. That's what I did for my OAM. Take advantage of their sale events too. You'll want to avoid cheaping out too much on certain motion components (namely pulleys and belts, possibly also bearings). For aluminum extrusions, a local supplier might be cheaper, especially if you can buy a long section and cut it yourself.
You could also look at the OG Star Tracker for a cheaper build, though I believe that doesn't support GoTo and may not have as good performance.
It's not "really" espresso but the AeroPress does make great small, strong coffees. There's a James Hoffman video on it. You'll want to use the inverted method (aeropress upside down, mug on top) for a short brew time, a large dose of coffee, and relatively little water.
IIRC I used 18g coffee, stir immediately after pouring 90g of water, then after 90s I flip the AeroPress + mug and press. You don't want to use a ton of force or you'll end up with a really bitter taste.