Los dos centados mios:
If you're looking to buy a used rental/demo raft from a shop: now is the best time, as you'll find some stores selling their demos, ie:
If you're looking to buy new raft from a shop: now is probably the best time, some decent end of year/inventory reduction sales happening
If you're looking to buy used from a private party - right now there is a good selection of used rafts - but if you wait another few months when demand is at it's lowest - you can likely find better deals, sellers more willing to drop the price. Especially if the economy stays the way it is or worsens - there could be more people looking to sell for cheap prices.
Side note: CKS (link above) has a demo 9.5 NRS Otter SB raft for sale for $1200. A small boat but tons of fun and a good price.