Genesis are still cheap, easy to find, care for and find games for.

Saturn are expensive for North American ones, and now even the Japanese ones are more than 100$ on ebay (they used to be like 50$ less than 5 years ago). The games are all getting way overpriced, even for very common one.

Dreamcast is getting expensive, but I think with some luck it might still be possible to find them around 100$.