With that budget I would get a Dual PowerLab8 with a bump controller and two 24v 55 amp 1320 watt power supplies and have money left. That way you can sit in the comfort of your lawn chair and check the charge status of your batteries with your phone!
http://www.usastore.revolectrix.com/Products_2/Cellpro-Dual-PowerLab_2/Cellpro-Dual-PowerLab-8x2_13
http://www.usastore.revolectrix.com...l-PowerLab_2/24-VDC-55A-1320W-Power-Station_2
Now that I told you what I'd do with that budget, what I'd really do is a single PowerLab 8 with a Bump Controller and a single 24v power supply for around $600.