Open Road has a number of mysteries on sale for $1.99 at Amazon US. The splash about it says these are "deals featuring previous winners and nominees of the prestigious Edgar Award."
The link for Amazon US is
here.
(The link is horribly long and messy, but I don't think I see any affiliate tags in it...if someone does, maybe some moderator can fix...)
There are a number of quite good mysteries in this bunch. No idea how long it might be good for.
EDIT: I randomly checked a few at BN and Kobo US and the prices seem to be good at those sites too.