Cheap Cheap!

SWMBO's compulsive purchase of "buy one get one free" Christmas lights was great value until it was realised each required 3 AA batteries and not mains 240V. Now the lights have dimmed it doesn't look such good value.
Consequently a new set powered by mains electricity has been bought; 200 lights on 20 metre of cable, enough to go 10 times round the tree and up and around the pictures!
Lo! Another wonder of sino-technology but not quite a rabbit on the moon.
Costs to date:
Tree £10
Cheap lights £3
Not so cheap lights £29.99
Must be a lesson in this somewhere? Probably find out when the next electricity bill arrives.