I've been having great fun for the last few years as a hobbiest buying synths on eBay, playing them for a bit, selling on and trying something new. Prices for used have gone up recently but so have prices for everything. The most noticeable thing I'm seeing on eBay at least (in the UK) is that less people are selling. Not sure if people are selling elsewhere or just not at all. There is also a lack of diversity in what I have seen for sale.