5ofus,
I'm not clear on where you're getting your ideas about this "upgrade"...

The bike is an unusual material, with composite main tubing but aluminum stays. My approach would be to maintain the 2 x 7 speed character of the bike, but to alter the gear range to something better suited to your riding style.

Possibly swapping the 53T chainring for a 50. Swapping shifters/brake levers for a new set of Shimano A070 Tourney combined shifters. Wider range cassette, changing from 13-21T to 13-28T, and replacing the chain, too. You'll need to add a cable stop on the downtube.

That way, you'll have lower climbing gears and a more reasonable cruising range. Your parts costs will still be ~$250 (Shifters - 110, cable stop - 10, cabling - 25, chainring - 45, cassette - 30, chain - 10, plain cork tape (please) - 8).

The cheaper option would be to keep your shifters and brake levers, and only replace the 7-speed HG freewheel and chain. You could keep that under $85 with new cabling thoughout, and tape, of course.

Don't make this more complicated than it needs to be.