Chronic undercharging will be pretty much equally detrimental to any batteries you get, and it results in a steady decline in available AH, which consequently means a increase in the power demand relative to bank size, and the depth
of discharge when the batteries are put to use, multiplying the effects.
In short, I think, also, if you are stuck in this position buy cheap
and replace as needed, because your other option is to buy $$$ and also replace. A good battery will be a waste of money. I think your best deal is to spend the least on the battery, and save up more for the system. Get the cheapest maintenance-free auto/RV battery from Wal Mart, or Costco, or K Mart [...or Canadian Tire..].
added: Call Trojan and ask for a distributor in your area, then ask the distributor for a dealer. Trojan is in Calif., and freight costs are just thru the roof these days.