2 Different database or 1 Single database I have a Windows 7 machine running MySQL database and I have a Linux machine running PostgreSQL database.

Preferably I would like to have only 1 machine housing both database as currently they are co-located in a datacenter which counts the electricty power and space used.

Would it be favorable to run 2 different database (MySQL and PostgreSQL) or convert the MySQL to a PostgreSQL?
Following up on @JonathanFite's comment, current and future resource usage is critical to answer this question, specifically memory capacity and I/O write performance.

Rule of thumb: if both databases can fit in RAM with room to spare, run both engines. If memory is limited, consider migrating the smaller database of the two, to the engine running the larger one.

Because you're most concerned about hosting costs, it will probably work out cheaper to consolidate, but you may have to increase your memory down the line.