My dishwasher has recently started gurgling when draining. It's been brought to my attention that my sink and dishwasher do not have a vent. How hard are these to install?

I don't think it's the dishwasher's talking to you. It sounds more like the trap that's doing the gurgling. You may cut in a upright tee and install a AAV(Air Admittance Vent) in the upright branch but all the gurgling means is that the dishwashers venting, (sucking air) through the water in the trap. Unless you can smell sewer gas out of the sink drain then this shouldn't be a high priority on your "to-do" list. Regards, Tom