How long of rails do you want? Industrial Metal Supply (IMS) has the 2" x 2" structural angle in 8' lengths for about $70. If you can find "rems" they are about $3/lb. If you sign up for their email, you can get killer deals with coupons.
Lately, we buy two 36" lengths from McMaster-Carr, it's more expensive per foot, plus shipping. But when you factor in time and mileage, it works out.
Make sure that you get the "structural" angle, with an inside fillet radius, and not the architectural angle.
