I brought a Cagiva, city 50 1998 model 11 months ago with 512km on the clock (now 5200 km) for £750. I commute 15 miles an day to and from work through town & country roads, it have been very reliable usually first attempt although if I don't start it up for an week it struggles to start. It's quite nippy for a 50cc bike (50 mph ish on an flat) It'll beat most cars off the line to about 10 mph (good for city/town).
Bad points: the suspension's very soft and the 10-inch wheels don't like pot hols and it's only an nifty 50 so it's screaming to keep up with traffic.
Economy: very good 75 mpg with average use, 80 plus at sub 30mph speeds. I use fully sinfetik 2-stroke oil (which it gets through quite fast). I love this bike but I wish it was an 100 cc with stiffer suspension but I'm not going to modify it because it's worth more standard and I'm upgrading to an Kawasaki zzr 250 In a month.