Without specifics (like what you're looking for), I'm not sure how much help anyone can be. Like any shopping, some places will have good deals on some items and charge too much for others.
But if you are in the US, Velcro I can help with! For manufacturers, Velcro makes the PSA stuff in 25 yard rolls, and the sew-on stuff in 50 yard rolls (widths vary). You can also buy the dots in various sizes, also in 25 yard rolls. Note that the "hook" and the "loop" pieces are sold separately, so you'll have to buy both kinds. At one point I needed a bunch of the stuff for the group home I ran; we had a local manufacturer locate a distributor, and got the stuff wholesale. Contact [email="firstname.lastname@example.org"]email@example.com[/email] and ask for information on a distributor in your area, or from whom you can order.