Best (and safest) place to cross the border is Lukeville, south of Gila Bend, which is on I-8 about halfway between I-10 and Yuma. There is currently an ongoing war between the Mexican drug dealers and the U.S. Border Patrol. Several people have been shot recently. Mexico in general is not as safe as it used to be, but the border is really bad. If you cross at Lukeville, you can blend in with the tourists going to Puerto Penasco.
I won't spend more on a bike than I think it's worth, but if it's a good deal, I don't seem to have a problem buying bikes I don't need.
2002 Vulcan 750, 2013 Royal Enfield B5
2001 XT225, 2009 Genuine Stella
1980 Puch moped