if the cue is nice and worth keeping and investing in,you can have a cuemaker cut .020" or so off the cue near the warp.most likely that will straighten it,you will also have to have the shaft taken down or a new one made.obviously a re-finish will be the initial investment and then whatever the cuemaker charges to cut the warp out and the shaft work too.$200-$400 range depending on the shaft.
only catch is it may move again,but it also may stay straight forever.anyway some cues built these days can truly benefit from being slightly thinner in certain spots too,imo.
if the butt is out pretty bad,i wouldn't worry about buying a new shaft and hoping it straightens it together.