I bought mine from Mustafa, about $40-50 for the large sheet cant remember. I think on the same area as all the party stuff, balloons etc...
There are different colors, % of light streaming in etc... for you to choose from. Very easy to apply also, just practice a few times ok already, if make a mistake, waste a bit of film nvm, at least save on installation costs. It won't ruin your windows as well. I got professional to do for me before, it is not perfect also, but maybe cos i found an irresponsible company. Nonetheless, can try it out first since it is not that expensive (depending on the size of your windows) as compared to seeking professional. Of course i will still prefer to engage professional to do if i got spare funds!