Look at Craigslist from time to time. Buying a complete and working used ebike is the cheapest way to own one.
I wanted a bike that could be used on hills as well as flats and pedal OK if the battery is exhausted. A mountain bike met this requirement. Low enough gearing is especially important on a direct drive hub bike, because of the drag of a hub motor. But, the gearing also has to be high enough for effective pedal power when using the electric motor. Because a gear drive hub can freewheel it is an attractive option, but is limited in power output.
Power: based on recharge times, I'm using 200 to 300 watts for most rides. Motor is an Aotema direct drive, front hub motor. Note...a direct drive will require some electrical power all the time, except descending, because it can't freewheel. A gear drive hub motor will require electrical power less of the time and so you will use less average watts. My ebike speed is in the 12 to 16 mph range, using a gas bike my speed is more in the 15 to 19 mph area.
The Aotema front hub weighs about 15 lb, the battery pack is SLA, 36V, 12ah, it weighs a bit over 25 lb. You definitely feel the mass of the front hub when riding, not so much the mass of the batteries that are mounted atop a rear rack.
Range, first ride was 13.2 miles, the battery indicator on the thumb throttle still showed green. Recharge time was 4.75 hrs, using a 1.6 amp charger. Average amps was 6.1, average watts was 221, 7.6 ah was used, about 63% of the battery capacity and calculated range using all 12ah is 20 miles. Because the batteries are new SLA and I want them to last, 13 miles is a good maximum range. So, the ability to pedal home easily is important.
Hobby King sells Lipo batteries, I use them for RC planes, helicopters, quad copters, cars and boats. For $145 I can get three batteries, each will be 3S, 11.4 v, 8.0 ah capacity. Weight for this battery pack will be only 5 lb, compared to 25 lb for the SLAs.
Because only about 8 ah is usable in a 12 ah SLA pack, and all 8 ah are usable with the Lipos, range should not be any worse for the Lipos.
Battery power output: SLA batteries are made for low power output, Lipos are made for high power output, there is less chance of harming Lipos than SLAs during an ebike ride. Both SLAs and Lipos are harmed if you discharge them to too low a voltage, Lipos are more sensitive to this than SLAs.
Hope this helps. Ask questions and look on Craigslist.
PS, my gas bike uses a Subaru/Robin on a Straton friction drive.