You'll have to look around online to find the cheapest place. I would start with ebay, amain hobbies, my atomic hobbies, and the RCU marketplace. If you have a coupon code Tower could be cheap too, but they're usually one of the more expensive online stores.

I was running one stock blue spring in each corner with 40wt oil inthe shockand one red spring in each corner with 50wt, and it did ALOTbetter than stock. However, I found some progressive rate springs(they range from 3lbs to over 7lbs when cycling) on ebay for really cheap so I put 4 of those on where Ipreviously had thestock blueones. So far it's been even better handling and hasn't lost any of it's jumping abilities. I broke an a-arm finally a few days ago though so it's been OC until I can go get a new one.

I keep my ride height set to a bones level stance too. This keeps it handling rough terrain like a champ and prevents it from wanting to roll as bad, but still gives you plenty of travel for jumps.