Less that and realistically what's the point of a lock on a half door.
One...it might slow people down from taking the doors... because time is the factor you use in evaluating security... how much time it delays someone from stealing something...
Two...slow people down from taking stuff from inside...
Three...I have a hard top I use in the winter...I use the soft top door tops and they mostly fit so come winter I can lock my jeep (more.)
I believe that's the one that has been linked to before. The other option would be reusing the tumblers you already have to rekey it, either lucking out and having most of the right sizes, or grinding some of them down so that they will work with the new key. If you only have some of the right length, you could rekey it with only those tumblers and leave out the rest, of course being less secure but $30 cheaper.
Either way, MountaineerTom's writeup on rekeying lock cylinders is a great resource and explains the process well enough that I'd recommend trying it on your own.