I went with stubhub and didn't feel like I was getting ripped off. I did go with expensive tickets (to me at least) since I was taking my mom to her first and probably only Rangers game she will get to go to. She still tells me it was one of the best times she has ever had. She loves baseball.
The Rangers through out tons of special pricing. So if you haven't already bought them and know the date, look for deals. I got $10 upper deck behind home plate one Tuesday plus $10 parking. We ended up in the first level about 15 rows off the field. Good luck and if it's a weekday game, plan plenty of time for the drive there. The Bush south of 635 is a nightmare.