It's nice to hear you have a good understanding of the cost and a willingness to spend what's necessary to make it enjoyable.
That said, I really would advise against the GBBR. Mags are finicky. Gun is finicky. Cold, even cool, weather is a problem. Sure the moving bolt looks realistic, and does provide some small recoil, but many people seem to have an exaggerated sense of the differences in realism. A properly upgraded AEG can be very nearly as realistic as a GBBR (including proper fire rate and stopping on mag empty with the use of a Trigger Master) and are much more reliable. The only real difference is the blow back, and even that you can get in an AEG, most people just don't consider the wear and tear to be worth it. But in the end it's your call. Hopefully you're happy with what you choose. Though if you're not, with the GBBR craze still going strong, you won't have any trouble selling it and getting an AEG.