I don't have a TM but how much are you really paying for a TM per time you use it? For the post part TM owners say a gallon of gas per hour... so 3 bucks to 6 dollars per use? The amount of time you save setting up and taking down a porty makes a TM seem beyond worth it... as soon as I see a good TM deal in the Chicagoland Area (Hint: anyone selling?) I will be getting a used TM... obviously there are repairs that are costly with a TM... but there is also repairs with a porty.The problem is you don't pay just once for a TM. You keep paying every time you use it.
So you either have to charge more, or make less money per job. Neither is that great.