Transit 1G wholesale in the right DCs is below $500 per port. 10gigE full port can be had around $1k-1.5k month on long term deals from multiple sources. 100g IP transit ports start around $4k.
The cost of transport (dark or wavelength) is generally at least as much as the IP transit cost, and usually more in underserved markets. In the northeast it is very hard to get 10GigE wavelengths below $2k/month to any location, and is generally closer to $3k. 100g waves are starting around $4k and go up a lot.
Pricing has come down somewhat over time, but not as fast as transit prices. 6 years ago a 10Gig wave to Boston from Maine would be about $5k/month. Today about $2800.
With the cost of XCs in data centers and transport costs, you generally don’t want to go beyond 2x10gigE before jumping to 100.