For MP, I get molds from the dollar store (decorative ice cube molds), from the craft store like Michael's or Joanns they have their candy molds, some of which have nice details.
There are some places online where you can used molds for cheap. Like here
http://www.facebook.com/#!/groups/280232832083663/You could see if there's anyone that has any to trade on here even. I'd offer to, but I just sold all my decorative ones on Craigslist.
Brambleberry has a nice selection of detailed molds as does Flexible Molds. (Those are my 2 favorite mold suppliers).
As for the soapsicles, some people use specific molds that come apart for those. I've always just used some inexpensive ones I found at a Dollar Store.
As for doing embeds in them, it would be just like doing embeds for any other molds.
Here's one from GoPlanetEarth
http://www.youtube.com/watch?v=YAx6fxoM ... ature=plcp