so i wanted the cheapest possible
Well if you have a PIC programmer the chip is about £1 (plus a 9 pin D Sub and a PS2 connector a resistor and two capacitors)
Anything else is expensive, using the original mouse is better (£10 would get you a "new, old stock" Amiga mouse)
but i would want a mouse wheel! does it need software to be installed also and would it work in every app/ early startup screen?
To activate the wheel and extra buttons then software is needed as the Amiga doesnt support it but the direction and two mouse buttons (sometimes even the third) will work without software.