I am partial to the Progressive Dynamics 9200. Made in the USA (Marshall, MI) it's a good unit that treats teh battery well.. You can get factory refurbs for around 200 more or less depending on the size.
Battery: My recommendation is one of two
LiFePo4 Battle Born can provide a special Progressive Dynamics converter that is programmed specifically for their LiFePo4 But as you have noted EXPENSIVE. thera are a couple other issues with LI batteries (They do not like COLD).
Good old GC-2 Flooded wet cell (OR GC-12) these are true DEEP CYCLE batteries ideal for RV use The GC-2 is a 6 volt so you need TWO of them in series to make 12 volts (They basically become 4D when properly wired). Treat them as you would a single 12 volt battery.
The GC-12.. IS a 12 volt battery
The 45 amp 9200 is the choce for a GC-12 45 or 60 for a pair of GC-2