OK, I do things really cheap...

4ft picket fence $30/pc
post $8
concrete $3
hardware $5
x 40= 1800
1 gate + hardware = 100
paint + supply 100

labor: bring in material + dig 40 holes: 3 guys 2 days. Install 1day. Paint 1day.
Total labor 12 labor days for $1000.

If you go fancier with vinyl fence, you are looking at $4-5k for material alone.