A good solid roping horse (not PRCA quality) around here will bring 5,000-10,000. PRCA roping horse will run you 15,000-25,000 one good enough for circuit finals. You can buy the practice horses that are half crippled from the rodeo guys halfway cheap, but you need to be able to take care of them, and be willing to spend the money for vet bills. I think ELBEE is right you won't generally find a horse that does both well and if you do, better get out the pocketbook. Barrel horses around here to get a decent one that will place you at jackpots here are at least 10,000. If you want a horse to go run or rope with the big dogs, they are generally 50,000-100,000+ (I know that barrel horses at the NFR are over 100,000 if you go to buy one at that level). You might check prorodeohorses.com they generally have a good selection of both roping horses and practice steers.
To Red: I would say there are characteristics that you want in both types, you want althleticism, quickness, sound mind, things like that. Don't have roping horses, but for a barrel horse I want mostly race bred, maybe a tinge of cutting or cow in them. Some racing lines make good barrel horses and some don't. The mare in my picture is 100% race bred and was AAA. She is bred to a AAA race stallion so we'll see what I get (only 10 more days until her due date (clapping)). I have her booked to breed to Frenchmans Guy this year and he is known to throw excellent barrel horses as well as roping/cow horses.