According to the 2003 Birnbaum's WDW guide there is a 2day Ultimate Park Hopper Ticket. $120.85 for an adult $96.48 for a child. I recconmend that you check the Disney.com website to check for the most up to date prices.
The length of the UPH is tied to the length of your stay. If you buy them in advance, you have to buy the UPH for the number of nights your ressie is for. If you wait and buy them at check-in, the front desk, at their discretion, can drop off the first or last night on the UPH.