For the more serious eme effort, power of 500 watts output or more is recommended. Commercial amplifiers are available that will give power outputs of 1KW and more. Many eme operators build their own power amplifiers. The 2 meter W6PO 8877 amplifier has been built by many, and performs with exceptional results. The ARRL handbook is a good reference for home construction of other amplifiers.
Kits are also available at times.
Check the classified advertisement section of QST or other ham magazines for kit suppliers or for used amplifiers. As I said before, you do not need high power to listen for eme signals. Listening is a good place to start your eme experience. Signals are very weak echos reflected from the moon's surface. Signals are usually at the noise level, or even buried beneath the noise, ocasionally rising above the noise for brief periods.