I like this one. It's cheap and comfortable and good for more than just dust. Those disposible masks never fit well and they really add up.
you should be able to find this model or one like it at many places.

Here is a link that might be useful: Mask

You might check out the Magic Arch N-95 mask that looks like a surgeon's mask. They come in a box of 35 for $25. They say they provide protection from tuberculosis, SAARS, & other airborne particulates (you would think that a virus would be smaller than cement particles). They adjust to any face shape (beards might be a problem).

You can see it at the site below, but you might be able to get it at a medical supply place near you & save shipping. A guy at another board was saying how much he likes them. I am going to find some, but don't have any personal info yet.

Sue

Here is a link that might be useful: Magic Arch N-95 mask