How far are you going? This makes a huge difference. If I had a commute of 5 miles or under, I would have gotten the cheapest thing available and charged it up at work.
...Some guy on an I-Zip was keeping pace with me the other day. In fact, he accelerated faster from the stops than me, and I had to catch up. He had a 350 Watt motor. I looked those up after going home. Bike with motor and battery can be below $1000.