Congrats! I think you'll enjoy the build process (hopefully, despite the frustrating moments) and the feeling of fishing with a rod you built.
As for finding cheap parts, I've gotten some nice, functional reel seats off ebay for $15 or less, some from the Roger guy who sells blanks as well as from Angler's Roost. Other than that, shop around a bit - JS
Stockard and acidrod are two I use. Add your parts to the shopping cart and compare totals. Another one is Utmost enterprises, they offer discounts on some items and charge real shipping rather than set rates. Shipping is one thing that can get you, if you order a couple parts here and there.
Some other advice, if you use a black rubber winding check, order one or two larger and smaller than what you think you need. They are dirt cheap and if the measurement was off you'll be glad to not have to order another one and pay shipping again. Most of the parts are cheap - guides, winding check, a couple spools of thread, hook-keeper. I buy cork rings and make my own grip, but you can buy them. I don't use special reamers to widen the opening in the grip, just use my drill carefully. I built my own wrapping jig for the price of a little lumber and screws and bought a cheap 22rpm motor and built a drying stand.
Buy razors from a home improvement store, they're cheap. After that it's epoxy and finish with mixing cups and brushes. Don't get the minimum you need of these items. You want the freedom to mix up more if it's starting to set before you're done or if you need to add another thin coat. It might cost a bit more initially but it's better than having a rod with poorly finished wraps.
Hope that helps. Definitely ask questions!