I actually went on ebay a second ago to price the cheapest new parts specific to the groupsets in question no cassette crank brakes etc that you polly have personal preferences for. For sram shifters and derailleurs. For shimano bar end/bullhorn shifters, derailleurs, 5 port junction, and battery. It actually costs $600 more for di2 which is approximately the price it costs me to feed myself and girlfriend for 2 months on 100% organic food like vegetables n shit gotta stay healthy bruh ya feel me tryna be potent here lol. A lot of bikes do not have internal spots for battery or junction so you have to take that into consideration for aerodynamics. I also looked up the weights of those parts and added them, assuming the shifters weighed the same short cage derailleurs, it's about half a lb more for di2 not including wiring and possible mounts. And idk a half lb in actual mass might cost you like a minute or 2 in an im, any extra drag all those extra parts may or may not be making depending on the rest of your set up could negate the pretty minute advantage that bullhorn shifting gave you for the extra $600.