Ow please stop it already with your pro 2000 campaine, we all know how you feel so lay off! The 2500 can hardly do what he is asking for... you won't find any PCI or PPC for the A2000 model and AGA is a bonus on the A1200 side. What casing the Amiga is in have nothing to do with this project obviously since he is aiming for a tower.
PPC will probably cost you around 120$ for the 040 model card. An alternative to Mediator is to get hold of a true Z3 bussboard and use a PrometheusPCI instead. It might not be as professional looking but it will probably be cheaper and get you more ports, still quite expencive though in the 150$ region I suppose. One can always buy a fat PC tower cheap and try put the Amiga inside instead of buying the overpriced Amigatowers (30$). Then there is all the other things like memory, harddrive, the PCI graphiccard, ethernetcard that you can take from (in some case older) PC's.