We booked four Airmiles tickets London-Calgary on Westjet back in March and paid roughly $600 for the four of us. We used 6400 miles and as it would have cost us upwards of $2500 if we'd had to shell out the entire amount, we were quite happy with what we got.
As many of the taxes and fees are fixed and not based on the length of the flight, your numbers shouldn't be a lot different.
- Mike