I asked this same question over at the Wizkids site and I figured I would here too.

I have $100 to spend on building a RD army. What units should I snag to build a fast paced army that is close to a swarm?

Not that I'm really an expert on this matter, but if you want to swarm the enemy, the Rasalhague Dominion Sylph might be useful for basing enemy 'Mechs before they get to you. It probably won't hurt to get multiples of the other Rasalhague Dominion Battle Armors as well.

I was thinking along those lines. Sylph + Gnomes in R10 + Undine in R10....

I like the Raptor and the Hod for fast movers. The Headhunter is at the top of my list for reliable RD mechs followed by Frigga, Scourge, and Kodiak.

I want at least two R10s and 3 Sylphs. I love Gnomes so it will be interesting to see how these play out.

I've got a Rasalhague Dominion R10 myself. Pretty interesting transport vehicle, with that gun turret it looks a lot better than the first R10 with the missile launchers. Since it is capable of dishing out 3 pulse damage after having been dealt a certain amount of damage, it really deserves the name Infantry Combat Vehicle. It should work well in firing formations with unloaded infantry.