"Has anyone worked with a pro studio to mix their tracks?"
Yes...
I was in a similar situation about 6 years ago so here's my story.
I had three songs that I just didn't think I could massage enough (final mix/master/lead axe) to my satisfaction.
So, I sent three songs to a buddy of mine in L.A. (Ted Perlman) who ran Buffalo Sound which he has since changed to 'The Ranch'.
http://www.tedperlman.com/I'd known him since the early Cakewalk (Sonar) newsgroup days back in the mid 90's.
I was comfortable with the (3) tunes and the raw tracks I'd recorded.
He said send him the raw tracks on a CD at -10db levels and he'd do the rest.
He also added lead axe parts on (2) of the them which is one of the main reasons I'd considered this route for these songs.....I was sure my lead axe work on these would NOT be good enough for my liking.
I got a great deal and I was very pleased with the end result and felt they were now worthy enough to add to my soundclick page.
Incidentally, I also drove to LA and had worked with Ted on a different project back in 2003 or so therefore I'd had the familiarity with him and knew his abilities and who he'd worked with.
Carry on....