First, Lion Av is an excellent group, Gregg does my stuff.
Second, I just bought a 65" GT30 and the THX mode was very good out of the box. If you look at my thread on it, you see where I posted charts of THX mode as found, and the grayscale error is very low, as well as the color chart looking nice. So, if you are tight on budget, I may recommend trying THX first and see what you think, if you do not like it, you may not like a pro cal. The other thing is, the GT30 is very limited on calibration controls, so they only thing someone can do is tighten up grayscale a bit and maybe get a little more out of color.
For someone anal like me, Ill have Gregg out in a bit to tweak it, but for many, THX mode looks nice enough. Also keep in mind the tv's shift over time, so as you get year after year on it, it will lose it's accuracy. I have my own meter so I have been calibrating my Samsung every 3 months, but yearly is fine if you are paying someone to do it.
Also, before calibrating, have you installed the 2.1 FW Luminance Patch? Have you checked to see if yours is a model that us pre fluctuating brightness fix? All things to do before getting a pro calibration.
Teachsac is also right. Even in THX mode, you will find contrast too low for most, and brightness was too high on mine. These you need a test pattern for, and I like DVE and Disney WOW.
Finally, look here for other ideas on who to hire:
http://www.thxvideotech.com/forum/showthread.php?542-THX-Certified-Video-Calibrator