the vinyl sticker shops I know of often had used panels on hand
in different sizes of signs they had taken down. Same as 1/2" and 3/4"
primed and painted MDO. but the ACP is so much lighter !! (and more $$$$).
I would not suggest buying new material from a sign shop - as they put their
ridiculous markup on top of their price.
be prepared to pay hefty coins for good quality panels. the cheaper panels
from China, such as Alibaba, will delaminate due to inferior adhesive.
it's a tradeoff of quality vs price.
I googled "aluminum composite panels, raleigh nc" and saw several sources you could
at least get some quotes from for comparison.
for vertical projects such as lockers and doors, you can use .020" metal both sides.
for horizontal surfaces, such as floors, the minimum I would suggest would be .040" metal
thickness for both sides....... again, you will get what you pay for.
there is also aluminum and plastic edge trim available for the thicknesses of the panels to cover the raw edge.
what size was the sheet that you said was $200.00 ?? a 4x8' x 1/2" does not seem unreasonable to me.
Note: Alupanel, Alumalite and DiBond products are not structural. they can actually be cut with a box knife.
so pay very close attention to the thickness of the metal clad.
when I did "vinyl" signs, I used 6mm Polymetal that is sold in Florida.
https://www.easternmetal.com/signage_extrusions-aluminum_composite_material.html
but that was many, many winters ago and don't remember the prices.
.