You need a vacuum pump with a manifold to connect to the same AC fittings where you'd put your recharge bottle. I suppose someplace that sells pro-type tools, but it'll be expensive. Couple hundred $$???

Leaving the air in there, your AC will sorta work, but not as cold as it should be. Moisture in there along with the air gives you more corrosion, and maybe it'll freeze in the expansion valve. Then your compressor will over-pressurize & destroy itself.

Seems to me you can do all the repair work, then go to an AC shop just for evacuation & charge. That's gotta cost a lot less than having them do the whole repair.