I believe I paid around $125 for the set of four. Bought them at my local mom-and-pop lawnmower shop which sells Exmark mowers. They had one of their $9,000 rigs in there and I checked the seat out very well and asked them to order just the isolators for me. Got them in by the end of the week!
They add .75" lateral and .5" vertical travel, really make a huge difference. The only issue is that they cannot simply be bolted on, they have to have a certain type of frame to sit in. Nothing a quick trip to the metal shop, a little torch work, and welding couldn't take care of.