Hello,
I would share your interest in flying very cheap tickets to get extra miles...sometimes it works out best that way. One of the best places to look is www.bestfares.com. It costs $60 a year. Lately I have seen round-trip fares for say $60 or so. There was once a DFW-MEM fare for around $20, but it only lasted a couple of hours. The fares change all the time as well. There used to ba one-way fares from DCA bo BOS for $67 with tax included. You could fly DCA-EWR-CLE-BOS for $67 each way. Years ago I remember a fare BOS-MHT for $19 on Business Express (at the time DL commuter airline). There is talk somewhere on this board about a DL $20.02 fare...not sure what it is for. May check DL forum myself.