If you do it by yourself, you save more than half price than whatever the contractor ask for. no matter it is metal fence, wood fence, or PVC fence. $20/foot you can finish all.
The most expensive part of PVC fence is the door and post.
3~4bags cement/hole is normal; you need dig more than 3 feet. If the PVC post is 8feet long, then you can only put 2 feet of the post underground. One bag concrete will be poured under the post with a metal bar in the middle.
$3.49/bag mixed concrete cement is best for this.
You can rent a augur during weekend from Friday to Sunday, the price is for whole weekend, $75.
Should you have any more question, you can ask me.