Since your goal is to be ready when THE DEAL comes along, I suggest that you do want a slider. Just a manual one, and then it won't matter whether you actually needed it or not. It doesn't hurt anything to have a manual slider and not use it.
I would also suggest you go with an inexpensive slider, like a Reese for example. It may not be the hitch you want forever, but it will get your new trailer home and get you started on your first few years of towing. Easy to sell it off if you later decide you want to upgrade. You can also remove the slider base and swap in a fixed base, if you find you don't need or want it.