RTV would normally work just fine. The only problem with that idea however would be with the alignment of the lower pan bolts, both front and rear. I doubt you could even get the bolts through the holes without some oversize drilling.
I'm with you, I would not pay NH's extortionist prices. There are plenty of aftermarket alternatives out there for far less I'm sure. Or, I would go to the local auto parts store and get a length of gasket material and make my own. Either way, don't support NH parts price gouging.