If you're not in a hurry, just use Philpost. They are way cheaper than any alternative, and if you pay a little extra (registered mail) they'll give you a tracking number and the risk your mail gets lost goes down to close to zero.
Rate is 125 Php for up to 20 grams, or 175 PhP for up to 50 grams.
Here's my recent experience, which shows it's not even slow (much faster than in the other direction, my mom's Christmas cards mostly arrive in March

 

For a 100 Pesos, send 2 to increase your odds of it getting there, depending on how much the delay will affect you. Send them on different days, too.