Diesel 6-71

Get a price from NAPA auto parts ..
Look the batteries up on line .
That’s a high price .

AGM batteries are fantastic.However, they are expensive compared to typical flooded batteries. If you are just starting mains and running a bilge pump, and on a tight budget, you don’t need AGM’s. You also shouldn’t buy batteries from WM in my opinion. Much better prices out there as others have already mentioned.
Be careful with power walls and other Lithium Ion batteries. They have great applications but not all are good for starting batteries as you may not get the cranking amps. You also need specific chargers and I doubt the alternators on the old Jimmy’s will do well with Lithium batteries.

I have 2 banks of 3 group 31 batteries paralleled in my 44 Viking with DD 6-71 TIBs. They handle starting and house with no problem.
I do have a 60 amp battery charger.
I needed them all replaced last summer and the guys that store and maintain my boat got them at a local auto supply.
They are commercial grade batteries and they were about $125 each.

They were about 7 years old when changed. The previous owner spent a lot of time on anchor in north channel of Lake Huron.
I bought the boat in late summer 2018.
All chain rode and 55 # Rochna anchor on
Ideal winch.
No separate batteries for winch.

Oops. Windlass.