I had to pay for my gear mainly coz the school didn't have anything in my size! the cons of working at a JHS? xD
BUT, having said that, you will most likely be asked to buy your own uniform and shinai even if you can borrow the school's armour. But it's cool to have and not too much considering how much armour costs. xD
Total cost for me was:
Uniform (hakama+dougi) = about 20,000yen
Shinai+bag = 4,000yen
set of armour = 67,000yen
For the armour though, I had to get the University (foreigner) size which was more expensive. If you can get away with the high school or middle school size, it's cheaper.
Same goes for the uniform, if you can fit into JHS or HS sizes, it's cheaper too.
Quite expensive to buy the stuff, but I'm interested in it, so it's probably worth it for me. If it's just a once in a while thing, I would probably ask when you "try it out" if you'll need to buy anything. Also, the kendo shop guy was super nice and gave me a nice discount on the armour (6.7man is the discounted price, btw).
I'm interested in Kyuudo too, but not sure where my closest one is atm. I'd imagine it being a little bit cheaper as you'd just have to buy the uniform (hakama+the top bit) and the bow and arrows and arm guard? Or something like that, but the uniform is probably a good investment and looks kakkoiiiiiiiii! xD