Mopar ...
I'll make the assumption that this fence has no function other than to mark a boundry? i.e. not meant to keep things out or keep things in.
Cedar .. pros, can be cheaper than other matierals CONS: cedar posts in 3ft holes won't last as long as some other materials due to wet rot.
Pressure treated pine posts or locust will last 20 yrs or longer. Posts are usually sunk 3 to 4 ft, depending on soil types.
For your application, the rails could be cedar if its cheaper. You'll have no stresses on them other than weather and split rails are easy to swap out.
In my region, a 3 rail split rail fence with PT pine posts at 8ft centers and cedar rails sells for about $8 p/ft installed. NOTE: these are pre-Iraq war prices.
Hope this helps out.