Sure, no problem with using the other aspen...as long as it IS Aspen.
I used to buy the Kaytee Aspen from PetDumb in the BIG bags for all my animals before I found Harlen Teklad at the RMREs every 4 months or so. And a bag of that is only a dollar more than the stuff at the store and I believe it amounts to more in the bag as well.

As for the pet store thing... oh I could tell you some stories. Even now, when I go in for supplies, at least half the girls working Pet Care (including reptiles) refuse to even open the snake boxes let alone touch the snakes. And we're talking young snakes here... sigh.