Hey Farmer,
A few thoughts, start at scrap value for these batteries. Base price is 10c per pound. I would say those batteries you are refering to are the 100A19 rated at 896Ah @ 8hr and 1020Ah @ 20hr. These 3 cells together weight 470lbs yielding a scrap value of $47. Be aware though the because of the 2% cadium content in plates of these cells most local recyclers will not want to touch it with a 10ft pole (so you maybe doing the seller a favour and paying him to boot). If the batteries are less than say 6-7years old their is most likely still alot of life left in them. Don't get me wrong I am a fan of these batteries, I have about 3 sets of them right now and two of them have been running my house flawlessly for the past 2 years. I got them for free though. I have a bank just like the one you are looking at right now. If you can get the code that is dittered or printed in fine print that is on the top of every cell I can date them for you and tell you when they were manufactured. Personally I would not consider paying more than scrap value for them unless the seller can prove that there are no problems with the cell by carrying them through a load test at least a couple of times. I am sure you dont want to end up with a couple of tonnes of batteries that you local recycler would not take from you even if is for free.
Cheers....
Damani