The deep cycle batteries from wal mart get pretty good reviews for the most part. I don't think you will be able to get a battery and good charger for under $100 though. Get yourself a good charger and it will last a long time and help your battery to last a long time too. Probably looking at $60-90 for a good battery depending on what size. I just bought a group 31 from academy for $90. It was the biggest that I could fit in my boat. I also picked up one of their 2/10/15 amp digital chargers for $60. It's fully automatic so it will never overcharge the battery.