Last pieces of the jig-saw

I have managed to find a very cheap DVD writer (about £15) which has 'lightscribe' capability, this will be the main CD drive for my 'Frankensteins Monster' PC that I am building. I am now bidding on a SATA hard-drive for storage - I already have a 80GB IDE drive for the operating system, and this will be my first venture into SATA drives. I have noticed that there are a lot of different sizes of hard-drives available which makes it tricky trying to find a bargain on eBay (the DVD writer is new, but the hard-drive will probably be second-hand).
I started with the idea of a 300GB drive, but had to also try 320, 350 and 360 to make sure I had the best price - I then noticed a couple of 400GB drives which were not more expensive (one even on buy-it-now) and then the 500GB drives didn't seem to be attracting many bids.
My resulting strategy (after failing to secure a number of 250GB drives) is to place some big bids on 500GB drives and if I don't get those, I will do a 'buy-it-now' on a reasonably-priced 400GB drive (assuming it's still available). This demonstrates how a 'buy-it-now' price can work in your favour if you price it right - it offers a definite alternative to the bidder and is fairly likley to sell way quicker...
My eBay rating is now 103 transactions (100% feedback) and I really MUST look seriously at flogging off the flotsam and jetsam of PC parts I have lying around in my loft..