Thats fair enough.
I have around 200 pdf on my pc, and the search takes less than 2 secs/.
I think that this software may only be useful as a free download packaged with something else, it may be expensive to advertise/get ROI. Or depending on your delivery and the software use it self - advertising/links embedded with free use license/trial, then upgrade to a no ad version for $19.95.
Do you have that currently?