It depends, as pointed out. Are you buying a loose stone or looking for pre-set things? Garnet is very reasonably priced and normally is found in larger carat weights in pre-set jewelry.
For example, this ring is over 2 carats of garnet w/ 30 points in diamond weight and is $300.
http://www.overstock.com/Jewelry-Wa...-TDW-Diamond-Garnet-Ring/2542209/product.html
I've never looked for loose garnet, but I would try to google it or maybe pricescope in the colored gem section has some online retailers to search. For the money, you'd probably do better w/ pre-set jewelry unless you want something custom, IMO.