I think 75$ hour is a pretty fair rate for a welding shop... but then again it depends on where you go... and if you're having a shop that can also do welding do the work they may charge more -- lots of auto shops are charging closer to 90 - 110/hr or more.
As for how long should it take to fit it and weld it. I'd say under 4 hours.
I used to be in the bumper business, sort of... either way I could probably clean up all the parts, tack, fully weld, rough and finish sand a bumper and double check all my work 4 hours, I think -- it's been a while. Either way 1000$ is over the top.
Also, they may not know how to finish sand that bumper... might as well just read up here and do that yourself. Less than an hour if you have a good angle grinder and some heavy duty thick flap discs and it'll save you a little money. It's just dirty...