Mex,
That's a fair question, and one I'm happy to answer. Mind you , I cannot make a comparison to AGM, only to FLA:
For the past two seasons, I have "full timed" May thru October (6 months out of 12). The plan was to use a 60a charger with my eu2000i and 430Ah bank. As it turned out, I ended up using my Peak 40a portable. This, of course, increased gen run times. However, using a 60a would have raised the gen's throttle, so even though run times would have been decreased, fuel usage would probably have worked out to only a little less.
I was charging, on average, about every other day for 3-4 hours. With the 40a charger, the Honda, at just a little over it's lowest throttle, was using ~ 1/2 u.s. gallon per charge. Until just recently, and over the past two years, I estimate premium gas has been in the $4.60 - $5.10 / u.s. gallon range; so about $2.35/charge X ~13 charges/month = $30/month in gas.
But that was all top end charging (~85-100%). So, yes, I could have done 70-85's and saved some gen run time, but ultimately I would have had to do top charging once a week, so charge times would probably have dropped from 45-50hrs/month to 32-35, for a savings of about $10/month. So, $30/month becomes $20/month. But at what cost? 100's of lost cycles, and the need to EQ more often.
With LI, I could cycle anywhere within 20-97%, and not have to worry about top charging, or progressive capacity loss, or cycle loss, or EQ'ing. As for run times and fuel costs, I estimate about 20 hours and $14 per month.
So compared with 85-100's, that's a savings of $16/month, using a 40a charger. Comparing the two using a 75a charger, savings would increase, seeing as amps would begin to taper almost immediately at that C/5.7 Rate (430/75) on FLA, but hold steady on Li.
Compared with 70-85's, that's a savings of $6/month, plus whatever is saved, not having the added cost of earlier FLA battery replacement.
I have not factored in solar because I cannot possibly estimate how much solar I will be able to make use of, in my particular situation, with parking at work, etc.
This coming year, I hope to full time 12 months a year, and estimate my Ah usage will increase by 100-150% during the cold months. And even though Solar will likely be even less of a factor, due to deeper discharges resulting in faster overall charge times for FLA , (in fact, ~ eqaul to that of Li at lower soc's), I do not think my monthly savings would increase much during the colder months.
