You Don't want an Aprilia RS50!!! They definitely do NOT do Italian bikes justice! They are nasty and generally all ragged (**read Shagged**)
If you are looking for a cheaper hack go for a Honda C50, They are semi-automatic (Via a centrifugal clutch) so they still have selectable gears. . . albeit only three they go the same speed as a Honda C90 (45mph) as they were made earlier than the C90's and accommodated a much better carburetion system.
Funnily enough they are classed as a motorcycle due to the wheel sizing, i.e. a scooter is classed so due to the diameter of the wheels, Honda 50's 70's and 90's all had 17'' tyre iirc.
They will do around 110mpg (mine did) and only cost me £80 to buy, £15 to tax and £100 to insure (Fully Comp)
The benefits of the machine far outweigh the cons i.e. its ugly!
Plus when you need spares you don't have to pay £150 for a chain and sprocket!
I had a 50 and two 90's and I think they are the best most bombproof bike out there and personally (as I M/C enthusiast) much better than the nasty expensive loud smelly two strokes out there.
I had/have:
Yamaha DT50mx '96
Honda C50 '76
Honda C90 '83
Honda C90 '82
BSA B25 StarFire 250 '68 (rebuilding)
Royal Enfield Bullet 500 indian (riding)
Hope that gives you some thinking.