Try souviner shops or resale shops and/or places that sell cake decorations which quite often have scale-like sizes.
In addition, also check the toy department of the big box stores, as well as any nearby "Pre-School" stores. The pre-school stuff will run about 3 for an arm and leg, but very realistic. Use the good stuff in the first 3 feet of view and the cheaper stuff farther back. If you have sculpting skills, have a look at some of Ray's stuff.
Tom Trigg
My husband is always on the lookout for O gauge animals, so I've learned some about hunting for low-cost details. Like PJM said, farm play sets have low-cost animals. Hobby Lobby sells "Toobs" of animals for $7-10 and many are large-scale-ish sized. Michaels has the Safari brand of animals that are decent but are much less expensive than Schleich brand. You can also use a 40% off coupon to get a discount.
If you have a thrift store, check the kids section. Our local St. Vincent dePaul bags up small toys and sells them for .99 each. I've found all sorts of goodies there.
Rene Schweitzer
Classic Toy Trains/Garden Railways/Model Railroader
Look at ones that are kid's play toys and come in farm play sets, not as detailed, but they are much cheaper. You might have to look at different "scale" sets because proportions are always different between the tractors, animals, etc.
Modeling the Bellefonte Central Railroad
Fan of the PRR
Garden Railway Enthusiast
Check out my Youtube Channel:
http://www.youtube.com/user/PennsyModeler
I've been looking for g scale or 1/24 scale animals for a farm scene for my Garden railroad. The problem I'm having is when I find some that look good they cost an arm and a leg. Does anyone have any suggestions.
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