I would prefer using 64GB or 32GB drives and put them in RAID0. Two through four SSDs can provide an additional boost in IOps, more won't scale good on windows and even hardware controllers, Areca is known to be capped at 70.000 IOps. While a good RAID0 array can go beyond 100.000 random read IOps.
SSDs are still expensive though; and with the NAND flash shortage that won't change extremely soon. But both the Vertex and Intel X25-M are known to provide good performance with latest firmware and reasonable pricing. Other competitors are also keen on bringing their own disks, but always check the controller chip they're using.
FYI: 120GB Vertex costs 320,- euro according to heise.de, so it appears ireland is a bit more expensive.