Not when you calculate the number of hours you can run them before they wear out...mine had over 7000 hours on it and paid $3500 for it. That is 50 cents an hour. If you pay $30,000 for a 300 hp and get 3000 hrs out of it that is $10 an hour.
At the end of each season, i find i use my kicker 5 times the hours i do on my main, so i concur with Profisher, except 3000 hours might be pretty optimistic.
I think a key consideration is "how far from port you travel to fish grounds and are willing to rely on your kicker to get home?" If you dont go far, 1 reliable main and one small kicker is my bet. But if you fish say 20 miles from port and oops, your main is down.... do you really want to rely on your 8 hp or 9.9 hp to get you home at 3-4 miles an hour, or slower if big current? For many, that is the primary reason many like big twins, so they have a viable get home. Having big twins makes it easier to manage as there is no lifting of the kicker up and down, better trolling a main when current strong, better tracking while boat mains are running on plane. Downside is who wants the maintenance of 2 big main engines, particularly when the hours get up there, and carbon buildup, VST tanks, thermostats, internal engine zinks, etc., all of which make boating/fishing less fun
If you fish far from port and want to use a 1 big main, plus a kicker that qualifies as a viable get home, there are now options in the new Yamaha 25 hp high thrust that came out last year, which i bit the bullet on and found if pushes my heavy 24' boat approx. 9 mph. No, it doesnt get me on plane, but a heck of alot faster than my old T8. It pure like a sewing machine just like the T8 and T9.9's when at trolling speed, plus has big alternator as well.
Anyway, that is my perspective . DAJ