scooter will depend on things like how tall he is, inseam, etc. and availability. and he will need to get it serviced in his area, too. so maybe find out if that will be possible?
if a SYM dealer is nearby used HD200's are a great buy and super reliable. and it will easily reach highway speeds. SYM claims 72mph top end, many owners say a bit more. idk what :"cheap" is to you but a good used example with low miles should be 2K give or take, depending on condition and owner and all those variables. i've seen 'em go for $1500. it can handle "adventures"
thats a tall wheeled scooter. for small wheels if he has a Kymco dealer nearby i like to recommend my model scooter, the Agility 125. it will "cruise" easily at 50mph under good conditions. anything more will vary accordingly. but this is just my pick for "small" scooter, not as BEST scooter. but its one that can be had well under 2K used and is reliable and durable and fun to ride and good for taller riders. super cheap used or around 2kOTD new with a two year warranty