For cheap batteries, check with the mobility type scooter vendors in your area. They have maintenance contracts on the scooters that require them to change the batteries often, and the old batteries still have plenty time left in them.
You can get them real cheap or maybe even free, just inquire.
I have 2( 4ah and a 12 AH) that are over 7 years old and still performing perfectly. The 4 AH is on my Preddy with the Kubota dynamo, and the 12 is on my Heald Bronco to start the 8 hp Tecumseh.
For a freebie charger, you can use any 12 to 13.5 dcv wall power unit from any old electronic device. Just have to monitor the voltage with a meter when charging.