Hugh, is half correct. If you are flying privately please contact the FBO, Fort Collins-Loveland jetCenter and they will assist you in arranging one. If you will be flying with Allegiant after they restart service in November then rental cars will be through Enterprises and yes the cars are on site but hours are limited to the flight schedule.
Yes, believe it's either Hertz or Enterprise. Need to make prior arrangements though as cars are not kept on premises.
Thanks! Your answer is awaiting moderation.