Depends on what you are medicating with. CopperSafe, for instance, is very cheap, and medicating a 45 gallon would be less than a few bucks. I got rid of ICH on two fish using it.
As for hospital/quarantine tank, the best idea I've come accross for a hospital tank is to make the tank as small as possible for the fish. If you're only going to have the fish in the hospital tank for a week to a month, it can be pretty small and the fish will be ok, if you're only putting one or two in the tank.
When you need a hospital tank, you can buy one or have it on hand. For example, for 30 bucks you can get a cheap 7 gallon acrylic gallon tank at Walmart with a light a lid and a filter. It'll work with most smaller fish. Fill it up with water from your main tank. Add two or three pieces of live rock from your main tank. You don't need to use sand or substrate. Pop the fish in and medicate. Monitor ammonia every other day or every third day and if you see it move up, just water swap (don't forget to add meds to water).
At the end of the medication period, you can water swap to get rid of the extra meds, and then pull the fish out to put back in the main tank.
Alernatively, you can keep a small backpack filter with ceramic material in it on your main tank, and then just put that on the Hosp tank when you need to use it.
As for getting rid of ich, I'd suggest two tanks. Put all fish in the first tank, which has no substrate, and hit them with coppersafe. Tank 1 can be just a tank with saltwater in it. In 8 days the fish are free of parasites (change water before day 8, if needed). On day 8, swap out 50% of the water twice per day for three days to get rid of as much of the copper as possible. Then take them out and put them in tank 2. Tank two can be just like the tank I discussed above, and can even be a small funcitoning tank with critters and all. Leave the main tank empty of fish for at least 3 weeks if any ICH infested fish were in that main tank, and 30 days to be 100% sure. Then put the fish back in. ICH gone. Guarenteed.