what is the best SAND to use in a run? I want to prevent BUMBLEFOOT

Sand will not keep your run dry. If your run is getting really wet, you need to do something about the drainage. Sand doesn't make the water disappear. The water is still there.

You need to either slope the ground away from your runs or put in French drains.

Maybe keep a tarp over the run if it isn't too wide.

 

I use red mortar mix, which is the yellow sand and not red. Your location may call it a different name or it may not even be quarried in your area. I live in NC.
It is the cheapest sand usually, and in the line of work I'm in I have easy access to it.
None the less get the cheapest sand you can find that is avalible in your area, with the exception of beach sand.
Bumblefoot is caused by the chickens cutting there feet or legs and it getting infected, do you have wire on the floor or sharp objects in the run or coop?

 

I like fill lime. It drains well, compacts well but not so tight that they can't dig in it. It's cheap... $7.50 a ton compared to $25 a ton for sand. Get it from a quarry. It is the small left over stuff after they crush rock so they want to get rid of it cheap.

 

I'm not sure that putting anything in a run will help bumblefoot. Bumblefoot is a bacterial infection that is invading an injury to the foot. You definitely do not want to put any type of sharp material down. What is causing them to get injuries to there feet? How high are the roost from the ground and what do they have to jump down onto from the roots?