It all depends on what you’re looking for.
If you want resin figures, often times buying direct from the sculptor/caster is the best bet, even overseas. USA sellers charge a shipping fee so honestly, it is sometimes cheaper to buy direct from Europe and Asia who make these resin figure kits.
There is Andy’s Hobby Shop USA online. I haven’t bought from them but I heard that they were pretty reputable and sell some of the rare Aftermarket items. You can see them on YouTube.
Always do a Google company review rating to see what buyers have to say if you’re in doubt and to avoid getting burned.
And most sales take place around American Thanksgiving and sometimes around Christmas (but most vendors are off and closed down for Christmas, thus no sales). There is probably one or two announced Spring and Summer sales, but for sure, Thanksgiving’s Black Friday weekend is the online sale to go to. Sales range from 10 to 50% off if you’re lucky to get 50%…usually it is 20-25% off for online sales. Some sellers have year-long discounts below MSRP and no sales at all.