I'm trying to clone a large operon (30kb) for expression in E. coli. I'm concerned that if I put this into a high-copy number plasmid it won't be stable. My first thought was to use a BAC or a fosmid backbone. I'm not sure how to go about getting a simple backbone for such a molecule however. I'd rather not shell out $400 for a fancy BAC cloning kit when all I need is the BAC itself. Any suggestions for a commercial source, etc., would be greatly appreciated.