soda blast is safest - it won't get rust off but will give you clean metal. The biggest is the skill of the operator. If he is under 40 i'd pass. The cost is based on how long it takes, it'll cost less to just blast the hell out of it and warp metal than if he is careful and takes the extra time to do a careful job. At 1K approx, it sounds cheap to me, i have frames done regularly and they cost about $400 each and that is done with black diamond, no finesse required.
If he comes to you be sure to ask about the mess that'll be left behind - remember, when they blast that stuff whatever comes out the nozzle is a one-way trip. It isn't gathered up and reused.