Hello and welcome to the forums! It is exciting that your mom is going to get you 2 additional budgies, but as FaeryBee stated, there are more responsibilities that go into it. If all 4 are going to be housed together, the flock dynamics will change between the 2 you already have. In addition to the larger cage you will need to buy to house 4, you will also need a quarantine cage for the new budgies before you can introduce them to your 2 existing ones. However, after you buy the larger cage then you will have 2 cages in all (the current one plus new one) so you could probably get away with using one of them as quarantine, though you may want to quarantine the 2 new ones separately.
I also have a fairly small room, so the cage I bought for my 2 Budgies is more vertical than horizontal. It is
a large cage, but I wanted my birds to have extra space. It is super easy to clean, looks nice, and has worked fantastically for me. It actually takes less time to clean than my previous, smaller cage. It is super easy to wheel from room to room or to wheel over so I can vacuum under it. I would highly recommend this cage. It has plenty of extra space for 2 budgies so I'm sure 4 would fit comfortably in it!
Here is the link:New Bird Parrot Cage Chinchilla Cockatiel Conure Large W/Stand & Two Doors | eBay
Here is a picture of it when I had just moved my 2 little ones in. (excuse the dowel rod perches as they had come with the cage and I put them in for a short time until I could get additional natural wood perches)
I bought it when it was on sale so it was a little cheaper (around $100). It may come on sale again closer to Christmas. You may also want to look into getting a large cage with a divider. If not all 4 of them get along, you may need to house 2 on one side and 2 on the other, or keep them in separate cages.
Such an exciting time for you and best of luck in figuring all this out!