Bit harsh...
If thats what you have always wanted and you can save your money well then I cant see why not. £700 is £700 at the end of the day and if one week you cant afford petrol then you dont drive, simple. If you really want something that much, you save, then get it!
EDIT: Can I just add that I had a simular response when asking if I should buy a supra and in the end I worked hard enough to save for one taking on every private job possible and in the end bought one. Things will go wrong tho even now I have only driven it for a couple of days since owning it and things did go wrong! I have spent more on the car than I payed for it and it still aint on the road. You just have to expect that with cars mate, there not cheap!