They aren't a premium, anymore.
Server rack batteries seem pretty economical. Just understand their surge current limit (designed for racks of computer servers, not inverters powering well pumps) and use a precharge system before connecting to inverters.
LiFePO4 battery manufacturers only exist in China, because no one here was interested in developing them. So patent owners gave an exclusive license (which has just now expired), and China ran with it. They are massively building out EV's there. The lesser performing batteries are good enough for our alternative energy systems and get used here.
The years you can get out of a lithium battery will be partly environment and charging, partly inherent in cell chemistry and partly quality.
I think AGM batteries cost $0.50/kWh of cycle life, FLA $0.25/kWh.
LiFePO4 server rack batteries appear to be $0.05/kWh, if they last 6000 cycles which is nightly for 16 years.
If that last 3 or 4 years with that sort of use, you will have broken even with FLA cost.
FLA forklift or Rolls Surette, you might get 20 years if sized for 3 days autonomy, mostly only discharged 15% at night.
LiFePO4, sized that large might age out before reaching cycle life. Cost could be $0.15/kWh. Sized for just one night's consumption you should achieve $0.05/kWh (and that only applies to power cycled through the battery.) Daytime you'd be using PV direct, or micro-cycling the battery (shorter life, I assume). Generator if overcast, unless massively over-paneled.
I do use AGM. 3 years ago, a fraction the cost of lithium I knew about, for a fraction the cycle life, ideal for backup. Today I'd look seriously at LiFePO4.