Cycling UK Forum

Hi, first time I have visited this forum and am seeking advice on purchasing a conversion kit. From what I have found so far is bike shops don’t sell kits to be fitted by the purchaser, I may be wrong but those around my area don’t. I feel I am more than capable of fitting a conversion kit. Therefore the only options seem to be eBay or Amazon.
There are lots of kits to choose from, my requirements are rear wheel drive and 1000w motor, as a pensioner cost is also an important factor.
Have any forum members bought from eBay or Amazon? eBay seem to be quite a bit cheaper like for like. Is a cheaper kit from eBay as good as the same named kit from Amazon? Like I have said cost is an important factor.
Thanks