I took your proposed prices and played a little - (I'm not sure why, other than I like playing with numbers)

The numbers you supplied delivers a best-fit straight line of Price=77.143*length+76.667, where Price is in $ and Length is in feet. This gives the following list for Price vs length.

1 $153.81
2 $230.95
3 $308.10
4 $385.24
5 $462.38
6 $539.53
7 $616.67
8 $693.81
9 $770.95
10 $848.10
11 $925.24
12 $1,002.38
13 $1,079.53
14 $1,156.67
15 $1,233.81
16 $1,310.96
17 $1,388.10
18 $1,465.24
19 $1,542.38
20 $1,619.53

Given that a 17ft kayak goes for $5000 or so, this is off a bit. You could factor in that a model does not have bulkheads, rigging, etc and maybe come up with a nicely finished full-size model should cost - oh, I don't know - how about $3500?

If you add 17 ft and $3500 to the list of price vs length and fit an exponential function to that, you get Price=167.8*e^(0.182*Length) and the following table:

1 $201.30
2 $241.48
3 $289.68
4 $347.50
5 $416.87
6 $500.08
7 $599.91
8 $719.66
9 $863.31
10 $1,035.64
11 $1,242.37
12 $1,490.36
13 $1,787.86
14 $2,144.74
15 $2,572.86
16 $3,086.44
17 $3,702.53
18 $4,441.61
19 $5,328.22
20 $6,391.81

I don't know if this is helpful, but it looks like your pricing is not all that high to me. Like I said, I just like to play with the numbers ...

Steve