For a minimum rate in Philippines, I would say you should target 1/2 (or 1/3 if cost of living is really low) of the rates a similarly-productive person would earn in the US. If you are unable to get even 1/3rd within the first 3-4 months, you should take up a job and improve your overall skills in parallel. You may find clients and people telling you 1/4th or even 1/6th is good enough - its a no no, not sustainable.
I work as a consultant and have also hired freelancers occasionally. Your expected rate is certainly doable. Even if you start with Elance/ODesk you can easily achieve $25ph pretty quickly if you can communicate well, and ask important questions. Also try to get long-term work at your expected rate and charge higher for short term work. I find it easier to get a fixed-cost projects at a better rate compared to getting a higher hourly rate.
2. When working remotely you have lesser chances of charging more than half the rate of a similar person living and working in the US (and with rest of the western world). Even if you charge half of that say $50ph, you are doing really good. Beyond that, try starting a firm and build local presence.
3. For money, focus on a particular type of work you can get good at pretty quickly. If you are an RoR person - stick to it. Allocate few hours if you want to do something like PHP or some strange new tech - just to learn.
4. Once you are set and earn a minimum rate comfortably, target not to work above 20 hours per week. Typically many people have degraded productivity above 24-25 hours per week. Focus on efficiency and improving it consistently. Leave the rest of 20 hours for reading, educating yourself, increasing domain knowledge, for hobby stuff and figuring out ways on how to charge higher :)
5. Write blogs, contribute to open-source, answer questions on stack-overflow, take up learning some bleeding edge stuff. I usually get a lot of work just because of these.
Market economics, opportunities, education, language and culture for North American region and Asian region is quite different and sometimes counter-intuitive. So when a US-based-person says "I can get $100ph fairly easily" - you should always introspect what/how they are doing differently.