Rent a Wrangler, take the top off and go 4-wheeling near Hoover Dam. Its a blast, just watch out for Bureau of Land Management officials!
BTW, $300 in Vegas can go faster than a blink of an eye. I budgeted $1000 over 5 days including 2-day Jeep rental, casino, and sight-seeing. I would have liked to have had more. (this included improvised on the spot hotel fees -$25 a night- since staying with a former friend fell through once i got there.)
If you do the typical bachelor party stuff, you had better bring more!!