With all respect Tom, if you've only got £100 in your bank, why are you even thinking about these final decisions?
Why not just save some more up, and then make the call.
I sincerely think that no matter what you do, or what you buy, at some point in the future you will end up buying that Marshall. So my advice would be to save as long as it takes and buy that Marshall now; otherwise you are just spending money you don't need to spend.