@nprofile1q... yeah okay i was hoping you meant cheap as in "just need one of em" not that it would possibly get blown up.
are you wanting a straight-up block which generates the square wave or are you okay with designing a clipping amplifier? I've only ever worked with discrete VCOs from Alps (E series 0dBm output, I'd have to dig for PN) and some random stuff from crystek.
my only experience with this kinda thing would be replicating some of Jim William's high linearity V-F converters. sorry ):
Very cool application though, I am excited to see what comes from it.