||If you're trying to keep costs down, headers aren't the way to go. Headman, Hooker and Thorley headers for a 440 motorhome engine will run about $350 -500 depending on the manufacturer. Plus you'll have to change the exhaust pipes from the headers back, either new or tie in to existing.
You also have to be careful when purchasing header that they will fit a 440-3 engine, which is typically found in a motorhome. Most cheaper headers won't fit the 440-3, only the car 440.
If you want to keep costs down look for a used manifold. Call a truck wrecking yard and have them look for you. You can also take the manifold to a welding shop and have them fix it. Today's products for cast iron welding are fabulous and they could probably fix it for about $35-50.