Is there a Technic set that is just an assortment of parts and not a specific vehicle?
Lego sells several kits of parts through their Lego Education line. You can buy them online in the US here: http://www.legoeducation.us/

The direct link to the Technic kits is here:
http://www.legoeducation.us/eng/characteristics/ProductLine~Machines%20and%20Mechanisms

They have a $50 "Simple Machines" set, a $140 "Simple and Motorized Mechanisms Base Set", a Pnuematics add-on set, and a very cool Renewable Energy set (yes, there is a Lego-branded solar panel!).

Also, if you look under the parts and accessories section (http://www.legoeducation.us/eng/characteristics/productType~LEGO%20Spare%20Parts%20and%20Accessories), you can order variety packs of various parts (e.g., 5 each of each length of the studless beams).

Caveat emptor: I have not compared prices to Bricklink.com, where you can also buy pretty much every Lego element ever molded in bulk quantities.