Suggestions for older pickup to tow 18k lbs 40'+ FW

neither your $10k budget nor your preference for SRW are going to get you close to a truck capable of pulling an 18,000 lb rig and 5 passengers.
double you budget and then you can choose between a used 1 ton dually or an HDT. the HDT gives you more power, more braking, more comfort, for a lower price; and turns tighter than a 1 ton dually.