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As long as you're using "dichlor" and not "trichlor", chlorine is fine. Bromine can be a lot easier to use, as it's formulated to be more stable in hotter temperatures than chlorine. This is why you find bromine floaters or bromine dispensers in many hot tubs. However, many people have a stronger allergic or skin reaction to using bromine. When I get my new spa I'm tempted to try bromine at first. If it bothers me I can always switch back to chlorine, which I used for many years without problems.
I just buy my chemicals at lowes.I use the dupont spa products. For chlorine I use the dupont pool chlorine in granular form. I bought a 25lb bucket for $83.00 Should last me 3-4 years by my estimation or even longer.http://www.lowes.com/lowes/lkn?action=productDetail&productId=232445-23132-10039&lpage=noneNow some people might think that pool chlorine should not be used in a hottub but I doublechecked the type of chlorine and it is the exact same type of chlorine used in the leisure time spa chlorine line.
Imo, it's better to have/start a close relationship with your dealer(i.e.- SUPPORT THEM) then to save $10-20 a year shopping online for chemicals. This of course is only for those that have dealers they actually like. Mine is wonderful, so I give them almost all my spa accessory business.