Bit late, but I can recommend the Salus SP600. You need to use the community driver for power reporting at the moment, but it's officially supported and the reporting should be fixed. I'm writing my own driver for it as well, just for the heck of it (and for presence detection).
They crop up on eBay occasionally for reasonable prices. Got one for £15 and one for £10 recently, but they're always there for normal sale at £25-30 if you're in a rush.
Oh! You could also use the AlertMe SPG100 smart plugs if you can find them. The driver I did can read the usage in Wh as well as the current power in watts, they'll do the accrual and can be reset to zero without having to pair again (just hold the button on the top until they reboot). They're battery-backed repeaters too, though you'll likely need to change the rechargeables.
