If you have local model shows that are held in your area, those are even better. Vendors sell off their stash at good prices. Buy raffle tickets too. Oftentimes they raffle off kits donated by vendors at the show. Check with your local IPMS chapter in your area.

This past October I went to Syrcon in Cicero (an hour drive from my home) and picked up 3 Tamiya 1/48 scale kits for $25 (F4F Wildcat, AM6M Zero, and Nakajima A6M2 Rufe Floatplane)

I also picked up an X-15 Experimental Aircraft for $10 and a decal set for $3. A raffle winner was a 1/72 scale pre-war German biplane. I may have picked up another kit cheap too. Came to the show with $60 spending money and went home with $10 or $15 leftover.

eBay is another source for model kits. I always choose Buy now option in the filters list and US only. I avoid getting in a bidding war. Key to the Buy Now option, watch for shipping charges. Sometimes you can place an offer. I often will click on Watch this Item. You might get lucky the seller will come back with a discounted price than his asking price on his listed price - usually 10% - 30 % discount. ALWAYS pay attention to the seller's shipping charges. Free shipping is even better if he lists it.