I don't think the problem is with the Mexico Postal system, the problem is with Mexican Customs - they want to inspect all packages, hence the high cost. That's why your friend sends everything to Laredo in bulk, to get cleared, and then shipped onward.

I checked with UPS in the US and they want about US$125 for a 5 lb package to MX. I have also been warned by friends that it is possible that half the goods will "disappear" enroute to me, haha.