What's a good flooring option?

[MarineHawk]

If you don't go with the concrete, you might want to go to the Carpet Exchange on 8690 Grant St. and see what they might have. I got carpet and laminated hardwood flooring there at prices cheaper than I could find anywhere else back in '02-'03.
I confess I don't fully understand what you mean about the bike/training/exercise issue. Are you simply storing the bikes in there and then riding them outside, or are you talking about stationary bikes? Forgive my ignorance.
I did the same basic thing you are talking about in our basement in our Thornton house with a pool table etc. I put half stain-proof carpet and half laminated 3/8 inch hardwood panels in there -- both from the Carpet Exchange. I also did my entire first floor with the latter.
If you're worried about damaging the flooring with your bike shoes, you might be surprised at how tough that laminated stuff is.
I also ventilated the basement during and a little after cigar-smoking by putting one fan on a window on one end of the area blowing in and another on a window on the other end blowing out. It works pretty well because you basically replace all the interior air and smoke with clean (except in L.A.) outside air probably about every 20-30 minutes. Thus, the carpet never smelled like smoke. In any event, a little smoky odor in a Man Room is probably a good thing.