I noticed that FireStop caulk is like $14.00 a tube. That seems really pricey.
I was told I could use Rock wool insulation but how do I hold in place for fireblocking and is it cheaper?
Any other recommendations would be appreciated also.
Thanks
Dave

With rock wool you will have to buy a lot and use a little. The cost savings probably not worth the bother. Use the caulking.

The material you need is called Mineral Wool, its used as a fire stop and is much better then any caulk. You can buy it at any insulation supplier. I don't think home depot or Lowe's will stock this stuff. It comes in pre-cut bats for use between the studs just like insulation. Just cut to size with a utility knife and push into place. Inspectors love to see it in all the open stud areas between the floors to keep a fire from spreading and yes it works very well.

Thanks for the answers guys. The building inspector said I could use Rock wool, so is it the same as mineral wool or different? I have some pretty good size gaps at the tops of the wall since the basement walls are not very plumb in spots, so I think it would require a lot of caulk.

when I purchased it last I received 4 bats that were 4'L X 2'W x 4"Thick. It was almost like a highly compressed form of insulation that can be cut to size and just pushed tightly into the cavity were you would like to create a fire stop. Cost was $40.00 and to use enough caulk to cover the same square footage would be insane, you would need 100 tubes or so.
I used it just like insulation bats in the cavities prior to sheet rocking

This sounds like "Roxul". Do a Google search.

Roxul is available from my local bulding supply place at a similar price to fibreglass insulation. You shouldn't have to phone too many suppliers before you find it.