Only you can answer that question. How much is your time worth to you? I have heard of guys charging from what the kit costs to many times that amount. I would suggest choosing a person from your club; don't play one against another, it shouldn't be a bidding war. You'll end up just offending everyone and wind up doing it yourself anyway. I see that it is an ARF so even with your mods there is only so much to do. Explain exactly what you want done, if your wallet agrees with his figure you have your answer. Having an experienced builder that can produce strong, straight and light vs. a long build on your own - well the answer is in how well it flies when all is said and done. It's all in the perceived value, if you feel it's affordable then it's the right amount.

Best of luck,
Dan