Don't know if you have Wickes or B & Q over there - they'd be the cheapest I'd imagine, assuming you mean electric lights - can't imagine solar ones would be much use over there, they're hopeless here in London in the winter, not enough daylight to get them charged properly.

I find that you get what you pay for with solar powered lights. I've got lots of cheapies and find that they stop working quickly. I have a few more expensive ones and they've lasted longer, "months/ years" wise and "hours lit up" wise.