I'm a little leary to post this, as most posts seem to be dominated by metal oriented people.
But have you considered epoxy vinyl ester/fiberglass? Most are good to 100C. If you want hotter than that, dual laminates are the method of construction of choice. Either a polyolefin or flouropolymer can be mechanically bonded to a fiberglass structure. Lastly, this type of construction can be stamped according to ASME Section X or RTP-1.
Fiberglass should be competitive in price to 316SS. I'm not familiar with the other alloy you mentioned. Dual laminates vary in price greatly depending on the type of flouropolymer used. A 12,000 gallon FEP-Teflon lined vessel is generally 20% lower in cost than Titanium Grade 7. This of course depends on size and the wildly fluctuating price of Titanium.
This is probably more than you ever wanted to know, but please let me know if you want more information.