+1 on the Luna Kits; I've got two and they're superb (my wife appropriated the first one after she took it for a ride). Find a bike on Craigslist for $200-$300 and you're set. You're going to receive lots of other opinions on systems and they're also good options. I have used both front and rear hub systems effectively for errands like you describe. They'll be in a similar price range.