Not knowing what you pay for your plastisol transfers, you'll need to make that comparison.
Adding to your points, beyond dwell, sub t-shirts can take longer in production as well due to stuffing "blow paper" inside and/or using pads or such to raise the print area to lessen press lines from the platen or from the sub paper.Cost effective decisions for dye sub transfers vs screen transfers also has a lot to do with the quantity of shirts being produced. Keep that in mind.
Plastisol transfers have a lower dwell time than dye sub so once you start getting into volume, the time involved for job completion can become a factor in your overall cost.
To add to MG's comment, you will need to consider the lint rolling process and when you screw up a shirt (and you will), the cost of a poly based shirt in comparison to a blend or 100% cotton is going to run you double to triple the cost in comparison.Adding to your points, beyond dwell, sub t-shirts can take longer in production as well due to stuffing "blow paper" inside and/or using pads or such to raise the print area to lessen press lines from the platen or from the sub paper.