prices are all over the place... if the batteries are not in living spaces you can use flooded batteries, in that case Golf cart batteries are the way to go.
Best price i found was from a golf cart guy i used before. I just ordered 16 of them for a 70 footer i run... owner wants a full day autonomy and that's going to give us 880AH at 24 volts... $89 a piece, delivered, plus $11 core charge. Exide is now charging core, normally $20 a piece but was able to get a deal.
I've seen them advertised at $150+...
it comes down to $1600 for the 880 AH bank at 24v. hard to beat.
on my boat the bank of 8 E3600 is going on 4 years, so far so good.