Driveway sealing: How long should it last?

Mr. Noddy has a weak spot for people who knock on the door and say, "We're in your neighborhood doing some work and rather than cart our equipment all the way back to ________, we'll be glad to do your driveway For A Price.

I'm weary of what I consider to be inept jobs by these men.

This summer I'm getting estimates and bits from local people who advertise in the local papers.

I'm in the Poconos. Typical winters mean months of freezing and thawing, snow and thawing, icy rain and thawing. In my experience, a sealing job should last for at least three years. Am I being unrealistic?

Also, can anyone give me a rule-of-thumb, cost per square foot? According to my records we've paid as little as $300 and as much as $950 (a particularly unsatisfactory job)

The driveway is 20 feet wide and about 120 feet long.

Mr. Noddy has a weak spot for people who knock on the door and say, "We're in your neighborhood doing some work and rather than cart our equipment all the way back to ________, we'll be glad to do your driveway For A Price.

Reuben, Reuben, I've been thinking
What a fine world this would be
If the men were all transported
Far beyond the Northern Sea!

Rachel, Rachel, I've been thinking
What a fine world this would be
If the girls were all transported
Far beyond the Northern Sea!