Reasonable price? No. Good? Yes. Clifford, Hooker and Aussie Speed all make them. Or you can hawk Ebay for some used stuff. Mopar Performance offered one at one time. Clifford offered an old 6 into 1 design years ago. My advice is to leave it stock or close to stock using a larger exhaust pipe on the stock manifold, because you are pretty limited in terms of power production, even with a 4 barrel and headers and other mods. It is after all, still a slant six and always will be. Unless you go some type forced induction or nitrous, you'll be hard pressed to see 250 HP. People build slants for the cool factor. Although there are cheap methods of turbocharging, that opens up a whole new can of worms for you to learn if you are not familiar with forced induction.
Not trying to knock the wind out of your sails, just being honest.