You should be able to get the 107 (internal) for between £70 & £80. Buy an external USB2.0 &/or firewire case for £30 - £40 and stick the drive in there yourself. This is all svp are doing and then charging you a premium for the service.
If you buy the external case all you do is take the lid off it and plug the DVD writer in exactly the same as you would if plugging it directly in on the PC. The external case is then connected directly to the PC (or via a hub) via USB2.0 or firewire with a single lead the same as for a printer, scanner, digicam etc.
I know I've done this type of thing 101 times before, but the cables will only plug into the correct socket and will only go one way around. Therefore I don't think it will cause any problems for you. The external cases should be supplied with full instructions to take you through step by step.
If you do have any problems then just ask on the forum as many others have already set up external DVD/HDD.
I've just had a quick look at the link posted by monkeynuts and although it isn't a case it will be a cheaper way of connecting an internal device externally - and should be just as simple, if not more so. It just wont look as nice.
Your dead right, it doesn't look as pretty but if you put the drive out the way on a shelf using an extention USB cable no one would ever know and you've saved enough money to buy a 25 pack of decent ritek04 dye dvd-rs!!