How cheap? every cent matters here, another point you need to consider is your budget, picking the "right" piece of mining gear isn't based on just one factor, you can buy an old  T9 for maybe 100$ and hit ROI in 2-3 months, but then you can only make about 2.2k of profit a day (before the power bill and rent) while consuming all those 70kw, on the other hand, you can get the 30w/th gears and make a few tens of thousands a month, but your budget needs to be so high and ROI won't be great, finding the right balance of everything requires a lot of information.

If you are able to provide this info, then we can talk, keep in mind that nobody will give you the "best" gear to buy, but at least you will be able to use the information to make an informed decision.