Shop around a bit. Seems like an Onan generator, transfer switch, box, and install should run about $5K.
But then I may be living in the past.....
edit: just reread your post, if you already have gen prep than $5K should do the job.
Dave & Jo Ann
2008 HitchHiker Champagne 35LKRSB | 2011 F350 Lariat 6.7PSD | Many great memories!