Don't waste your $$$

Yes, you can do it.  The Air Force has a ''Fixed Wing Qual'' course for dudes in that exact situtation.  Most are guard/reserve dudes, but I know a guy flying Vipers on Active Duty that flew Cobras first.

The only people that will look at your high school grades are: The USAF academy--with a D avg, don't even bother applying. The college that you are going to go to.  You need a 4 year degree to become an officer in the Air Force.  With a D avg, you may have to do some sort of Community college in order to be accepted into a 4 year ...

No, pilots need 20/70 vision or better as long as it is correctable to 20/20 (glasses or contacts).  Of course, everything is waiverable in the USAF. 

You should check out Baseops.net forums.  They have a lot of info on that site. I'll answer any direct questions you have.  I'll caveat that with--I'm an OTS grad and a fixed wing dude (going to the A-10).  If you want to be a pilot, the USAFA is your best bet.  Shoot me back with some questions.