Four player IPAC is $65, $69 if you want USB interface also
and from Ultimarc.com
"The I-PAC2 has 28 inputs. They are all programmable and are designated as 2 joysticks, 8 buttons each, plus coin1, coin2, start1, start2. One of the inputs is assigned as a shift key to access an alternate code set.
The I-PAC4 has 56 inputs. All programmable and designated 4 joysticks, 8 buttons each plus coin 1,2,3,4 and start 1,2,3,4. Two of the inputs are assigned as shift keys to access two separate codes sets covering the player 1,2 and the player 3,4 inputs."
So for four player ipac.. you still have 8 buttons for each player..