ebay is the place to go. I bought a very good pertol strimer there for 85 uk
it was quite large though at 50cc.
If your getting a mower dont buy cheap I have just bough 2 new ones and both are not up to the job - bewware of Flymo cheapies which have little plastic cutters not fit for the job and guess what you have to keep buying and replacing the plastic blades. Look underneath a flymo before you buy.