I want to share my cheap heat bed construction.
Two pallets 5e
A couple of boards 10e
Sand and styrofoam insulation 15e
Nylon fabric 3e
Carbon Fiber Heating Cable 10m 5e
Temperature Controller 12e
Manual labour priceless
So for less than 50e including waiter tip you can achieve 25C in heat bed and possibly more.
Free tip: put some wheels on pallets so you could move heat bed.