I have carried a small scooter around for a couple of years now and would not be without it. hard to be specific about model but if you want to buy secondhand take a look on Ebay, i have purchased two via this source now. Find a low mileage well known make, Honda, Yamaha etc. Although i have a 125cc i have used a 50cc and despite what has been said on here, provided you do not want to travel far it will be fine. Why would you be any more vulnerable than on a push bike and even on my 125cc most things still pass me. It is a little unsettling at first but all give you a wide berth and no real problems. Personally I would not even consider a trailer, if you want to tow buy a caravan. You should be able to find one well under your limit my 125cc Honda only weighs 99kg although my rack and towbar weighs around 40kg. I only have a small van, 5.75mtrs, but it carries the scooter with no problems and i still have 75kgs spare on my rear axle with half a tank of fresh water. If you need any advice on racks etc please contact me and will try to help.