Well, my favorite forces rarely consist of just one full lance/star, and in fact rarely include only ground forces. With the stated limitations, though, it would probably be 2-4 medium 5/8/5 'Mechs (Griffins, Wolverines, Trebuchet TBT-5Js, etc. or custom variants based on those chassis) anchored around an Awesome or Thunderbolt, with a flight of aerospace fighters (probably Transits/Lightnings), a lance of Bulldogs or Goblins, and if they'll fit into the remaining budget a small contingent of infantry.
Just eyeballed it since I don't play 10k a lot, and when I do it's usually because we're trying wacky (and very expensive) Manei Domini/Thuggee Phansigar/Society forces, or something along those lines.