I recently did that with US-05 and S-04. I plan on doing it with US-05 and BRY-97 soon. I wouldn't want to compare more than one liquid yeast since I only have the equipment to make one starter at a time but if I did that could be cool.
stirplates are cheap to build and erlynmeyers aren't that pricey... or you can get the gallon of apple juice fromt he store and use that. Way cheaper than an flask.