I have just been to my local Sainsburys and got myself 2 boxes of 20 LED solar powered garden string lights for £12.99, buy one get one free. The lights can be switched on and off and have a setting of flashing or just still. They look great on trellaces and give a nice touch to a warm summers evening.
There are lots of other varieties of lights for the outdoors, including coloured string lights and ones that have more bulbs but the prices go up where there are more bulbs e.g. £14.99 for a coloured set. They also had packs of solar powered lights that you stick into the ground. (sorry didnt see prices of these)