If you're going to buy stuff at a con, usually the last day is the best day to buy stuff, dealers will discount stuff so they don't have as much merchandise to bring back with them. xD
If you're local to SoCal, I'd definitely recommend stopping by
Frank & Son, get there early because parking is terrible (and bring cash!)... but this is 100x better than any Dealers Room at a con, you can find all sorts of rare plushies, model kits, gashaphon, etc. plus you can haggle. :D As far as online shops go, I've ordered some of my figures from
Anime Castle plus they do free standard shipping over orders of $85.