What do you consider tight?
(smiles at Biknut)
Is that a photochop job or did you actually mount a motor and the controls with no way to drive the wheel?
Cadillac makes very sturdy bikes but that model certainly can't me motorized as is unless you remove the rear disc. Even then it won't be very sturdy with the back cupped motor mount removed and the motor resting flat against the seat tube.
But back to the topic question...
Just out of curiosity do you want a mountain bike for the style or just the front shock? because if you have dreams of off-roading an MB you best think again unless you buy a $600+ bike like a Giant, and even then you better be prepared to make some serious HD custom motor mounts.
Trek's make pretty good motorized bikes. They have a pretty solid frame and the geometry is usually well suited to mount a motor.
I picked this 800 up for $50.
About Schwinn...
In 1960s America, the bicycle that every regular American child wanted (including me) was a Schwinn. In 1993, Schwinn filed for bankruptcy. The firm had been overtaken by imported Chinese bicycles. In 2001, a company called Pacific Cycle bought the Schwinn brand out of bankruptcy. Pacific Cycle, now owned by a Canadian consumer-goods firm called Dorel Industries, says the secret of its success is “combining its powerful brand portfolio with low-cost Far East sourcing.” Schwinn bicycles now line the aisles at Wal-Mart.
( The above taken from this page
A survey of outsourcing: Sink or Schwinn | The Economist )
I have built a couple Pacific beach cruisers and they are OK quality wise for $160 and up, Pacific however trashed the old Schwinn materials standards.
In short I am just adding my voice to the choir of voices you hear say stay away from any Huffy and any Schwinn made made after 2001.
Hope that helps.