Looking for inexpensive upgrade for bunk mattresses....

If you have some time to wait, check online places like amazon.com, buy.com, overstock.com etc. I bought an 8" thick memory foam queen size mattress to replace our crappy uncomfortable mattress in the RV. If memory serves I spent about $300. It is super comfortable, vastly superior to the bottom of the line mattress the manufacturer supplied.

I had to "notch" it out to fit around a cabinet in the bedroom. Since it is foam, no springs or anything, I was able to cut it to fit without any issues at all.