if all you want to do is simple stuff you can use any version of flash. It`s not until you get into doing stuff with action script (the codeing aspect of flash) that you have to really worry about versions etc. If i have flash player 9 installed and you use flash mx and build a swf for flash 6 then i can read it but someone with flah 5 will be promted to upgrade to the latest player.
As for worring about if everyone has or uses flash i wouldn`t worry to much. flash overall has a 99% penetration in the market and is a better choice versus using javascript.
As an alternative you can also check out
Swish Zone they have some lower priced stuff and editors which might suit your needs.