Friction drives are not too common in the kit offerings. I have seen a few friction drive motors only on ebay. They are usually 24v, but have seen some 12v offerings, stay away from those for efficiency. There are many good and innovative FD builds on Endless Sphere using R/C motors with the motor itself as the driver contacting the wheel. These are light/small and usually attach to the seat post and run on the smaller cheaper R/C batteries. However they require you to fab the installation. By far the easiest ebike to get up and running is a hub motor kit. If hills are an issue then a 500w kit would be entry level. The higher the voltage the better, but now your are into big and usually $$$(or heavy SLAs) battery territory . The battery is the $$$ of most bikes. I would build a bike with pedals so you can assist, otherwise you will need quite as system as it will be the sole means of power.
