I have two mountain bikes:

1- Next shocker, green with flat tubes, but otherwise excellent working condition.
2- Roadmaster Mt Fury, red in good working condition.

Selling both for $20. You can take the tubes of 2 and use them in 1. Or you can buy cheap tubes from Walmart and have two bikes.

The pictures are grabbed from the web. My bikes are older (~4 years) but are quite appropriate for campus purposes.