It depends upon the height and type of the tower as well as the location. On flat ground with regular soil, wind, and ice conditions, a 150′ monopole type tower can be built for around $100,000. Irregular soil, heavier winds or ice conditions will increase that amount. A lattice tower is slightly more expensive to build. Monopoles typically are only built to 200′, above that a guyed tower or a lattice (also known as a self supporter) will be needed.
Stealth type structures like artificial trees and church steeples cost significantly more. It is not uncommon for a stealth installation to run $300,000 total. This is one of the reasons why carriers choose to not build stealth towers everywhere.