I fitted the genuine BMW grips to my 2004 model R1200GS as it came without them from the factory. I replaced the non-heated grips for the heated version, plus the right-hand switchgear on the handlebars (to get the switch). This cost me about £220 in parts as I recall, then I had to get the dealer to make a change to the bikes software to 'tell' the bikes computer they were there.
I have no idea why my bike didn't come with heated grips as standard, as every other R1200GS I have seen since has them. I didn't want to fit aftermarket grips to my bike as there is something about the standard items that looks good and works well, plus I didn't fancy all the aftermarket wiring plus messing with switches and relays.
Fitting the BMW items took me about an hour (using the right small torx screwdrivers) as the wiring is simply plugged in, no soldering etc required. The throttle twist grip is easy to release from the throttle cable. I then asked nicely at the next routine service if they could enable them in the software, and they worked from then on.
The only problem I had was when on the hottest setting, the throttle would 'tighten' as the grip expanded against the bar end. This was solved by moving the switchgear slightly away from the grips.
Maybe you could source the parts from a breakers to save money, then get your local dealer to do the software bit during your next service.