1. There are a few with high prices but I don't think you find one with "redicules amounts of money" outside EBay. Having things on the shelf cost alot of money too you know.
2. Check
this site.
3. Most A1200 accelrators fit in the desctop though some require cutouts of the CPU trapdoor or it removed and some require bigger feets to lift it up some. If you are unsure then ask the seller. I recommend Blizzard cards over any other but there are meny that work reliable, I do however not recomend Apollo cards as there are loads and loads of reported problems with the cards. Check out
this site for more accelrators.
4. It is specialy made Amiga hardware so you can sadly not just take a PS2->COM converter from a PC.
5. Search the secondhand market for this joystick or C64 units with it included. As also recomended earlier the Sega (Maskersystem/Genesis/Megadrive) work as 2 button joypads on the Amiga and are realy strong.