A solid and attractive base for your printer, Granite
If you want a more solid base for your printer;( I learned from my big and tall Delta Rostock Max that it is important) and if you seek out a local kitchen countertop firm and stop by with a case of beer about clocking off time the odds are very good you will depart the location with some nice Granite cutouts that you can either use as is,or dress up with some work with a rental diamond wet saw....
while not as perfectly flat as a AAA Granite surface plate in a machine shop the ones I have tested on my shop AAB surface plate would grade about ABB for flatness and will I am sure be the flattest things in your house for most of you... mount three good rubber feet in a triangle pattern on the bottom and you will have a very stable printer... this may not be as important in a MK3 as in a Delta that is about a meter tall but if you look at the youtube video of the Factory tour that Tom Sandladerer gave of Prusa recently (you will see a couple of his printers set up on Granite surface plates....)
Where I live the going rate seems to be a case of good beer for about 2 or 3 sq feet of sink or cooktop cutout. you may have to do a bit of bargaining to establish the rate where you live. Small jagged pieces will be free in most areas and decorator samples in 16" x16" sizes are frequently given away when the parent slabs that match it are no longer available or end up as "crazy" paving for small patios.
it is worth pointing out that in some areas there may be an ongoing demand for Granite scraps or remnants and hence you might have to buy them (typically at about half the cost per square foot of the parent slab but this will include cutting down to your required size and the cost of the parent slab will be based on how attractive it is with kitchen designers at the time and other factors... it is amazing just how cheap some contractor grade granite slabs are.