The Grom is fucking tiny... Coming from me.
The seat on a Grom is about level with the seat on my scoot. Best bet if you want a dirt cheap, non-SM starter bike is a Ninja 250. They regularly go for around 1200 here for ones with like 4k miles.
Oh, and as for the Ruckus, highway speed thing.... GY6 swap. When we meet, a handful of guys ride the interstate to the meetup. That PY one at the top can do 75, the guy that built it (different person) has one that does over 80mph