Yeah, 6000s are great, I weld them all the time -- but they aren't T6 anymore after I am done. So if your structure is such that annealed strength is sufficiently strong, 6000s are beautiful, but that doesn't usually apply to bicycle frames that are not overbuilt.

With respect, head over to weldingweb.com or any other forum frequented by professionals in this field, and ask them how likely they are to accept any job from a person who tells them what they think it should cost. You will be invited to shop elsewhere. There is, in fact, standing mockery for customers who tell welders that "It's just a 15 minute job!"

Any shop and welder equipped for this job will be charging well over $100 an hour, and $50 barely covers stripping off the necessary paint. And "I did my own prep" is rarely, if ever, going to fly, unless you have a long-standing relationship with the shop. No shop is going to trust an unknown customer's prep work, because if there's any contamination, the job just became several hours of cutting, grinding, and cleaning, and then the shop loses their rear.