I have been talking to various people about bases for kits and at the moment these are the three that are in play.
They all work in slightly different ways and look different. If you are thinking about getting one, you will need to go to the vendor's site and read all the detailed information about them - this is just a pointer to them. Start with what you want it to do for you and then decide which one does it best.
Price-wise it will be a case of where you are buying from and what the delivery cost is to you
This all began for me because when I ordered my Petit Palais from Petite Properties I also ordered the very nice base that goes with it. I think it really finishes off the structures to get them off a (piece of furniture) surface a little way. It also makes for a good way to hide the electricals.