I'd do the concrete, it doesn't cost all that much here. $75/yd on weekdays, $85/yd on weekends.
350 ft length X 12 feet wide(my assumption) X 4 inches thick = 51.8 cu. yds.
52 X $75 = $3900
52 X $85 = $4420
plus labor costs, if there are any (DIY)
cost of lumber for forms
cost of tools...