Very nice card and I like the art too.
However, using CCT we have:
Dune Crusher
Cost: 5 (attack) + 1 (high hp) + 1 (ability)
Dune Sweeper
Cost: 3 (attack) + 1 (high hp) + 1 (ability) + 0 (upped)
I think the ability is about the same price as Warden's: it doesn't kill, it hasn't got a target, but it's automatic and doesn't require a cost. +1 cost for the ability is fine. So, if you want to keep the lower stats for the upped one, I'd suggest to decrease its cost by 1 or 2 more. A 3 cost would probably be too low, so 4 cost seems fine.