Over Christmas the best deals on the Moto G were with Amazon/Tesco/Argos - with about a tenner between them, but it was a case of whoever had them in stock (whichever of the three was out of stock was always a tenner cheaper than the other two). Then get the SIM separately. You just need to be careful you get the model you want. There are four different Moto G models (two discontinued original models and two current models) and the descriptions used by the sellers don't always make it clear which is which.
If I use the Amazon listing as an example, the latest pair of models are:
- Moto G 4G - the current shirt-pocket sized model, 4.5" screen, 4G compatible, single SIM, upgrade to Android 5 available, c.£130-£140
- Moto G (2nd Gen) - the current larger sized model, 5" screen, 3G compatible, dual SIM, upgrade to Android 5 available,c.£145-£160
There's not really a lot between them. 4G coverage is patchy at best, there are limited applications for dual SIM slots (possibly handy if you travel abroad a lot, or if you want to combine separate personal and work numbers on to one phone). Other than that the biggest difference is the size - the 5" might have the edge for use as a remote viewer but the 4.5" fits better into the pocket.
Whichever of the two models you should choose, the on-board memory is a bit short at 8Gb - but they'll both take a 32Gb micro-SD for extra storage capacity.