I haven't read all of the above posts, but here is why you should go with buying and Erlenmeyer:
1. You only need one container. Add the water, then the DME. The only things you'll need to sanitize is the tinfoil, and maybe the neck of the flask when you add the yeast. Simple as pie and reduces chance of infection.
2. Large surface area on the bottom reduce heat up times
3. Narrow neck reduces boil=-off to the point where you almost suffer no change in volume (I find about 50mL in a 1L starter is boiled off, which basically compensates for the DME you add)
4. Stir bars spin easily on the flat bottoms
5. easily accept stopper. My 2L flask accepts no. 10 stopper. I use a solid one for shaking, and a single hole one for my airlock.
6. Borosilicate Erlenmeyer flasks do not break when relatively large changes in temperature occur (in the range we are dealing with). I go straight from my stovetop, where the glass is well in excess of 100 Celcius, to 10 Celsius water. Never had a problem and I've never been worries
7. Bought mine for $20 at my Univeristiy's Chemical supply store.
8. Looks badass
You should seriously look into buying one. We are always looking for ways to simplify our lives as brewers, and this is one which makes starters a breeze.