I'd just buy 4 cans of Fluid Film, get the car up on jack stands, grab a creeper, and go nuts. Put a straw on a can and blow it into the door drainage holes at an angle if you really want.
Nail all of your locks with WD-40 so they don't freeze up and to clean them out.
Much cheaper and probably takes only 30 mins, and you inspect for rust at the same time.
The only time I'd research for the best undercoating place in your area is IF YOU PARK IN A HEATED GARAGE.
The reason I'd be inclined to DIY is a lot of these places employ kids who focus on working fast to make the boss happy. Then there is the possibility they do a quick pass to get the car dripping and smelly, then stick it in the lot for you to pick it up.
This is a waste of my time and 100+ dollars in my opinion. Unless you stand there and watch to your satisfaction.
Also, do all of your maintenance on your car that you plan to do before you go (oil change, fluids, etc.). You don't want to work on a car that has just been undercoated, very messy.
It is very important to put Silicone lube on all your door and trunk seals before you go for undercoating as well. This is to prevent the undercoating from melting your door seals if any overspray gets on them. I use Wurth Silicone in the tube that says you can use it on brakes when you lube slider pins etc.
I really do say that doing it yourself is best, as I have heard of places using old engine oil from their own waste tank for the undercoating. This motor oil may have old prestone, brake fluid, ATF etc. mixed in as well, and you can have big problems with your paint and door seals afterwards, so find an honest place, don't cheap out.
If you park in a heated garage, i'd wash the car weekly with a wash and wax (the wax added to the soap would help repel water a bit, and wash down your side windows into the door and leave a waxy film down there too, all while removing abrasive dirt and salts, and minerals).
I'd rinse out the wheel wells extremely well, even up top, and the shocks, brakes, etc. Spray heavy amounts of water on the windshield cowl (the vents just below the wipers) to melt any ice along that tray that may sit there, and rinse out the dirt and salt out of the drainage for your windshield.
If you don't undercoat anything and park in a heated garage, buy a flower watering wand where you can extend the neck 2-3 feet, put it on jet, and spray the whole underneath of the car.
Don't do this if you undercoat, or take it to an automatic car wash that sprays under your car, as you'll wash away the oily protective barrier.
Also, research a new car you plan on purchasing. A Honda may be less prone to rusting than, say, a Mazda of the same year. So research a rust belt car and be a bit choosey, that could save you on many rust issues without you even knowing about it.