Not sure if one exists at that budget but looking of a mount cutter at that sort of budget. I have a logan basic one but Mrs 645 paints watercolour and was looking for one with a guide etc.
I have a Maped one (I think it's usually referred to as a matt cutter) which, depending on how long a guide you buy, comes in at about £100. Seems to the job very well. I think Hobbycraft stock them.