I go by what I seen on a budgie forum that states that a single budgie should have about 3,800 cubic inches to live comfortably. So with the current cage you have your budgies in, you can fit two budgies, three is pushing it. I personally have my 'tiel in this cage: http://www.wayfair.com/Prevue-Hendryx-F ... P1059.html
(the picture doesn't do it justice) and have my six budgies in a simular one. If you are pressed for space, I suggest this cage: http://www.wayfair.com/AandE-Cage-Co.-D ... MgodZmQAww
It's a bit pricy, but looks like it would be good for your situation. With this cage, you can comfortably fit about five budgies, and it would be roomy enough for a 'tiel or two.