Well, the good news is that they made a lot of coinage. Random bronze or silver coins, especially if they're not in the best of condition and with dubious provenance, are kind of cheap. The museum-grade stuff, that collectors really want to have, is quite fiercely bid over when it comes to market. And they never made a lot of gold coins - the value was impractical compared to the cost of goods and labour - so that shit's expensive, yo. But if you're wanting a few denarius to call your own, then ebay's full of them.