I've been researching cheaper ways to get into resin infusion without having to splash out on an expensive vacuum pump.

Would a manual pump like this work?:

https://www.ebay.co.uk/itm/Engine-Oil-Brake-Fluid-Extractor-Removal-9L-Sump-Transfer-Vacuum-Hand-Pump/172659264201?epid=2164769182&hash=item28334b4ac9:g:I5MAAOSwBt5ZD-Xf

Some people who make RC planes use hand brake bleeder kits like this one:

https://www.ebay.co.uk/itm/HAND-VACUUM-PUMP-HELD-BRAKE-BLEEDER-TESTER-SET-BLEED-CAR-MOTORBIKE-BLEEDING-KIT/391718817400?epid=595953556&hash=item5b3442ce78:g:c48AAOSwB-1YuE1W