Just got my two budgies today and we went with a cage that the employee at our local pet store said was plenty big enough. After looking online I'm realizing I don't think it is (should have done that first I know). It didn't really look like they had cages as big as I want there so I'm looking to order one. Also is it ok if they stay in the smaller cage for a week whilst we wait for the order? Sorry if this is a redundant question. I really want to do the best I can for my little buddies.
My Piano 6 Ferplast is a great size for my pair of budgies.
It's 34 inches long, 18 wide and 27.5 high. The main thing you're looking for is the length of the cage, which is basically their flying space. For a pair of budgies, you don't really want it any smaller than that.
The cubic capacity of your cage is probably what matters most. Each budgie needs about 4000 cubic inches of space. So two would need a minimum of 8000 cubic inches.
To find out the volume in cubic inches of your cage, multiply the length, width, and height. So the cubic volume of the one you already has 5850 cubic inches.
The Ferplast Piano 6 has a cubic volume of 16, 830 square inches, so it's more than big enough for the pair (and they do love the space.)
I'm not sure where you live, so I can't advise on retailers, but a quick google of Ferplast should help give you an idea of price and availability.
Edited to add: Being in a slightly too small cage won't do them any harm in the short term.
If you order it right away, get it and set it up, you can probably carefully clean up the cage you have the budgies in right now and return it to the store. (Hopefully you kept the receipt?)
Most of the big box pet stores are willing to take the cages back.
If not, then the cage you purchased can always be used as hospital and/or travel cage. Everyone with budgies should always have a spare cage on-hand at all times.