These 18v battery powered cordless grass trimmers at Tesco Direct look good value at £11 (free reserve and collect).
Product Information :-
Keep your lawn edges neat and tidy with this 18V cordless grass trimmer. A 4-hour charge will provide on average 15 minutes run time so it is ideal for small to medium areas. An extendable shaft and 180º rotatable head allows you to cut back grass in difficult to reach parts of your garden. The grass trimmer has a telescopic handle and an extra, adjustable handle for 2-handed control. This trimmer has an adjustable cutting head with a 25cm cutting width, and uses an auxiliary metal wire. The trimmer features a double lock-off switch for enhanced safety.