I am amazed that you got 7 years out of those Trojan batteries.
I have no experience with them but I hear acceptable reports on the Wal-Mart brand batteries. I seem to remember that Sears had pretty decent batteries as well.
I can only assume that the cost is an issue. My personal recommendation is AGM batteries (Concorde/Lifeline). But they used to be 3 to 5 times as expensive as even good quality deep cycle RV/Marine flooded batteries. There may be some brands out there these days, that weren’t available several years ago, that have more reasonable pricing. As they become more popular, the prices should come down. I just bought a new AGM battery for a Suzuki S40 motorcycle from Batteries Plus that has worked out great. It was made by a Co. in China and was branded ‘Xtreme’. $70 versus the flooded original for $40. Try Batteries Plus, they can do the research and get you a fair price on whatever you chose.
The Group 29 Interstate deep cycle RV/Marine batteries are sold at many RV dealers and should be close to equivalent to the Trojans.
Have Fun!! Mark & Donalda 04 Horizon 40WD no TOW 90,900+ miles and counting
Triumph Bonneville & Susuki S40 on the back