Taardaan, I'm not sure what your soldering/repair skillz are like, but as long as you're searching ebay, you might find specialist places that will sell just the socket piece that needs replacing?
If it were me, I'd have a go... and if it really was "a special socket" (ie, proprietary connection assumed) I'd look to see if there's any way of bypassing it by soldering in more conventional connections (eg, RCAs, DINs,). But that's just me - I'm a notorious tinkerer)
You can also sometimes happen across "hardware wreckers' yards" that strip down f*cked consoles and peripherals specifically for the purpose of selling the parts.
I've done that before with certain pieces of kit (circuitboard for slim PS2 Power switch for example) and have even sold some stripped PC pieces myself (Gfx bourds, sound cards, jump blocks, etc)
I just did an ebay search for "Guitar Hero Cymbal" and there're a few replacement units
that came up for .99c, so you might get lucky if you keep a few watches.
You might have to bite the bullet and pay $30 for postage from the US, but hey, it's better than shelling out $500 for a whole new kit.