It costs nothing, because it's not a toll bridge. No one is moving mercantile goods through a Teleportation Circle. Not only does it require a high level caster, but the portal is of limited size and only stays open for 6 seconds. It's a terrible method for trying to move large amounts of goods or people...
Generally true ... except when you're creating a circle. You can use the castings at the time of the creation to send people, goods, etc... through the circles you create to help offset the costs.
It might cost about 500 gp to send a galley on a 2 week trip along the sword coast - carrying 150 tons of cargo. That would cover the cost of labor and the depreciation of the ship assuming a 20 year lifespan.
A wizard that wanted to use a 5th level spell slot (for teleportation circle) and a 4th level spell slot (for conjure mino elemental to summon 4 Ashen Warhorses) could drag about a half ton through a teleportation circle.
Now, you could say that the cost to ship that half ton on the galley would be about 1.66 gp. If you were optimal in your efficiency, that would work out to be about right. So, you might think that a wizard might only be able to charge a few gold to offer to have his summoned mounts drag a bunch of cargo through a portal ...
But ships are never fully efficient, and there are huge advantages in not having to worry about piracy or having to wait out a 2 week trip. Plus, the captain/owner of the ship will want to make a profit. All of those things add to the cost.
A wizard could go about collecting a few teleportation circle destinations and then setting about a small business to offset the costs of circle construction by doing transportation services to those circles. A clever wizard might expand upon those by having their flying familiar deliver mail or small parcels as well - or one with time on their hands could add dozens and dozens of unseen servants to the mix to carry goods through the circle (although anything they're carrying will be dumped on the other side as the unseen servasnts will disappear as soon as they pass through.
How much will this offset the cost of construction? That would be up to the DM and player to figure out - but a really smooth wizard might be able to offset most, if not all, costs of construction in my game.