It doesn't have to be that expensive if you are prudent with your usage during outages. We have a Bluetti AC-300 at the moment that is not tied in but will be this year with a transfer switch and additional Power Modules. It easily runs our oil furnace and blower motor. The system is expandable up to 12.5kw. We have 3 ecoflo solar panels that can be run in tandem and they are great as an add-on. One big plus for this system is that it can be recharged via your car/truck. Pull the car out of the garage, fire it up, plug it in for a recharge session. A lot easier than adding propane tanks for the few outages you'll have to deal with on average.

Good luck with your setup.