Since you mentioned a few posts back that you're operating on a budget, buy what you can as you can. It's better to buy quality items even if it takes you longer to get everything you need.
With that said, even though your rH isn't ideal you should still be able to manage a decent grow. Low humidity won't kill them, and later on they will automatically help raise the humidity as they fill your space and begin to transpire.
The VPD chart guidelines should ultimately be your goal, but in the meantime your plants will still survive.
@PK1 suggested a wet towel. You can also put a fan blowing on a bus tub
or similar filled with water. There are hacks that will get you by until you have the funds to purchase more equipment. The exhaust vent system should be high on your list of priorities though. It will help draw the air from the room into the tent.