For every $r>0$, there is a vitali set having outer measure less than $r$.
Here is my approach:
Take arbitrary positive real number r.
The interval $(0,r)$ has positive outer measure and hence contains a vitali set $V$(say)
Outer measure of $V$ is less than or equal to $r$.
But I need to construct a vitali subset whose outer measure is strictly less than $r$.
Do exactly what you did, but with an interval of length $r/2$.