The style of shirt would factor into the cost as well. You could do a basic tee or you could go to a fashion tee. The style will change the pricing since fashion tees are higher priced than the basics. If you were to print a different image in each of the 3 locations with 1 color in each location, you would have 3 screens. Each screen has a setup cost, plus each location would be priced at 1 color x 1 location. You could easily be $75 and up depending on where you go and how that shop's pricing structure is set. Screen printing is more practically priced for long runs/larger orders because with every shirt to be printed allows one more piece for the costs to spread out.
Let's create a hypothetical example and say that:
1 color (black ink) = $5.00 per location for 1-11 pieces
Screens are $20/ea x 3 screens
The white shirt is $7.00 for an XL
In this case, 1 XL shirt with 3 locations, printed with 1 color in each location would be $82.00
Now, if we did 11 shirts the exact same way:
1 color (black ink) = $5.00 per location for 1-11 pieces
Screens are $20/ea x 3 screens
The white shirt is $7.00 for an XL x 11
The total for the 11 tees would be $152.00.
Each tee would drop significantly to $13.82/ea
12-23 pieces would see another drop.
The costs are the same, but more pieces allow distribution across the entire order. We as screen printers also see it as a slight time increase to print the extra shirts since the screens are already done and the press is already registered for printing. The increased time to print is nowhere near the time to get it all setup and ready, so we are always more than happy to print more rather than less. The pricing structure allows profitability for the job, with true justification for the breakdown. There are times, such as your situation, that it actually DOES make sense to pay a high price for 1 shirt. Comparing a DTG or HTV print against screen printing can sometimes get you into trouble. Each process has it's advantages and disadvantages. Colors may be off, texture is different, and even wearability is different when a sample is sold and then printed with a different process. The reason is because it's a different process all together.
You can get heat seal labels made for you, or you can pad print, screen print, or sew a new tag in. HTV would be a pain in the butt to weed all the small stuff. There are requirements that have to be on the labels, like country of origin, fabric info, sizing, etc.
Perhaps somebody more proficient with DTG could chime in on the limitations, but I would think that if a platen is available or can be fabricated, you should be able to print anywhere as long as the surface is flat and the assembly can move freely without getting jammed in the machine?