If you have clients that require ProRes they you need to invest in a Mac. If it's just one client, then find someone who will encode the file for you. Otherwise, you need acquire the tools that your client expects you to have. You can get a MacMini for $599 and just use it to encode ProRes files. It has a Core i5 Dual Core 2.3GHz and is actually a nice computer (I just bought one not too long ago).
~jr
http://www.johnrofrano.com
http://www.vasst.com