Hi Keith,
Nice location, so close to the air base! Hearing performance teams is always a blast - I've heard the Thunderbirds a few times and it is always a treat.
If you're looking for a recommendation, I'd suggest buying the 310 ($150 right now) and getting familiar with it. You can always add the cable and software later on when money won't be an issue. Also, programming by hand will force you to get comfortable with your scanner.
I use an Apple computer, so unless I wanted to run parallel systems for Windows (which I don't want to do), I have no options for software. As a result, I've programmed everything by hand and learned quite a lot!
As for the rechargeable batteries, they are definitely a good idea but not a necessity at first. When scanning at home I use the included power adapter so I never waste batteries. When I'm out plane spotting, I'm on battery power and so far the energy usage has been very good. So, I don't have rechargeable batteries yet, but in the past few months I have only used two sets of batteries.
Hope your surgery goes well - a new 310 is just the ticket to recovery! This is
the cheapest I have found it including free shipping. I dealt with "Rick C" when I ordered and had a great experience.
Good luck!
Mike