My shower setup is a pepsi keg (extra from my homebrew stuff) with a schrader valve for the air inlet (can use any normal air input - compressor, foot pump, etc) and a sink sprayer with extra hose on the output.
Heat water, dump it in, pump it up and enjoy. Doubt I have $50 into it and it's rugged as hell. Weighs very little and if space is at a premium, you can stuff it with 19 litres of soft stuff for transit.
Also - if ever I upgrade/change direction the keg will always be worth what I paid for it so I will never be out more than the cost of the filler valve, hose and sprayer. So $15 after years of awesome showers.