I remember freshman year with my one betta. My room was at one end of the hallway, the restrooms were on the other side. Dx You could check your local craigslist for used Minibows. You can also check Walmart/Target for plastic totes. I use a sterilite show-off for my delta, it hardly bows. It comes in smaller sizes too.
Check it for leaks/etc, and rinse the inside until the water runs clear. A piece of cardboard or craft mesh can be used as a lid and cut out as you want to fit heaters/filters. It sounds kinda ghetto, but I love it cause it works. xD Do you use any substrate for your tank? If it's possible, you could go with bare-bottom instead, and keep your 10g. Just spot clean with a turkey baster and then a water change, rather than going through everything to siphon debris.