tank size is LxWxH divided by 231
So your tank is 6.5 gallons
I would keep your eyes open for a cheap/free 10 gallon to hold you over until the 25 gallon tank is free. I have found them all over the place for very cheap and you can buy a new one at Wal-Mart for like 13$.
Find this 10 gallon Basic Aquarium for your fish at Walmart.com. Save money. Live better.
Turn the 10 gallon on it's end and then you have the vertical space that would be just fine.