2 halves of a Black Reach set are indeed perfect. Find an Ork player to split with or sell off the Orky bits on eBay, craigslist, bartertown, or whatever.
That'll give you:
10 Terminators
2 Captains (easy to convert into other characters)
20 Marines (2 missile launchers, 2 flamers)
2 Dreadnoughts
At a minimum that's 1180, plenty for a good starter army all for around 75 bucks.
After that, I'd recommend 2 Rhinos. They give your marines necessary mobility and protection. Kit your Captain out to be a Librarian, scavenge bits to give 2 of your Terminators cyclone launchers
That should add up to:
Librarian w/ Null Zone, Gate of Infinity
10 Terminators, 2 w/ cyclones
2x Dreads-multi-meltas and heavy flamers
2x 10 Tacticals, missile launcher, flamer, combi-melta, Rhino
1200 points even. From there you can pick up a pair of Predators and Speeders to round out your army and bring you up to 1500. That's a good array of vehicles, flexible weapon sets, and giant unit of Termies to take any punishment thrown their way.