Oh I get you Jamie!
Just don't fall into the trap we did with our rented cottage. We only intended being there for 6 months, so I didn't want to pay for insulating the loft (the landlord wasn't interested). However, I wish I had done, as it would have paid back within a year, and we stayed there for seven freezing cold winters in the end!
I guess you either need to do it cheaply from whatever you can source for free or nearly free, OR do something better that you can take with you when you have to move on!