I think the need for highly reflective tent walls is a holdover from the days of flourescent’s, CFL’s, HID’s etc. Those light sources - even with reflectors, had a huge percentage of their light output going somewhere OTHER than to the plants. That made it very important to try to make use of all that wasted energy by trying to reflect it back to where it was needed.
Modern LED’s - especially strip type LED’s are far more focused. They do not send very much light off to the sides and none of it goes up. Here is a typical radiation intensity graph. This is for the LM301H.
The vast majority of the light energy goes down - not to the sides - and none is going out past a 90 deg angle or up.
This means there is far less need to go hog wild about highly reflective side walls or any area above the height of your lights.
That said, there is still some light thats going to hit the side walls, and you will be increasing your efficiency if your side walls are reflective However, I dont think its nearly as important a detail as it used to be in the “old days” before we had cheap, high efficiency LED’s. 
I personally quit worrying about polishing the side walls of my tent after I put in my LED light. I clean them between grows, but I dont care about water spots, smudges, old pieces of tape, etc etc. It just doesnt make a significant difference - especially if you use strip lights that are spread out evenly over the grow space. Just dont under size the lights, and use dimable drivers, and you will be fine no matter what you do with the side walls.
Do the best you can, within your budget, but dont go over board. Save that money for some other aspect of the setup.
Edit: Ha1 @BudSy beet me to it!
Edit #2: check out this thread by @Mr.Sparkle for everything you need to know as far as designing a great LED fixture on a budget.