I use a Joule pre & several different power amps with my VSMs. The right SS amps actually sound great with this speaker - the bottom end really firms up. (And who among us doesn't enjoy a firmer bottom end?) The TAD Hibachi monos are a very good match - and they're priced in your neighborhood. That said, I, too, usually end up going back to tubes with the VSMs.
Prima Luna monos are a good tubed choice at your budget, and allow for easy output tube rolling. This excersize is really rewarding with Merlins because they are unusually revealing of any upstream changes.
Marty