They are two VERY BIG variables right there. Which one is cheaper when under utilised or tickets are too cheap? Yes I thought so.
I can operate a Cessna 152 much cheaper than either with 50% load factor? If you are in business to lose the least amount rather than generate the most you can then it's going to end poorly. I'd probably lean towards CRJ 900/1000 if I was going down that path, at least you get a $40mil aircraft for $15-20million and lease costs that reflect it (the last runs of CRJs were heavily discounted to try and spool up sales). I get why Alliance uses the E190s, that's a different reason to what Bonza is doing, they need the performance specs to go into the clients strips and still have decent range, CRJs are more limiting in that regard.
Everything in context: Alliance's model is built on having a whole stack of spares available, which is what they had huge success with in buying the Fokkers from Austrian years ago. The ones that are being broken up are some of the oldest that were operated by JetBlue, and what they have found is that they are paying more because they have more green time on the engines and other LLPs than expected. That has changed the value equation, and the high demand (and replacing the Fokkers) has pushed more into service before they get chopped up.
All great until an AD comes out on your old fleet that effectively makes them useless and worthless....Fokker 50s anyone? It's free, here have one.....please take it away...please?
PS just looking at some burn figures the 737 Max has marginal fuel burn difference to the E190, so the only real difference is going to be lease costs, and since the Max is brand new I assume you will have warranties and guarantees as well keeping maintenance costs down, which on a 10 year old Embraer airframe you'd probably have to do what Alliance is doing to keep costs down, hence why they are so cheap to acquire.