How many scouts and adults are going? Having run the numbers for similar youth group trips in the past, the tipping point for a chartered bus was somewhere between 15-20 people. For groups of 10-15 renting a van would probably be more cost effective. You could potentially split the group into 2-3 SUVs or minivans (if you have the adult driver), but then your fuel costs are going to probably offset the savings over the rental of a single large vehicle.
Have you checked out the Philmont Reddit page? You might have some luck finding another group to partner with there. There may also be some related travel tips too. https://www.reddit.com/r/philmont/