Quote: "it's over 1600 lines of code"
It's not to break down your project or anything, but 1600 lines isn't -that- much...
But I guess if it's a stable engine and your features don't lack usability... I'm not going to say anything.
And about the price:
Maybe you should compare it to other programs.
Some prices of TGC distributed programs (the ones around the price you want to go):
Enhanced Animations -
$29.99
ConvSEO -
$29.99
DarkLights -
$25.00
Unity -
$20.00
EZrotate -
$19.99
Enhancements Expansion Pack -
$25.00
TextureMax -
$20.00
Nuclear Glory -
$24.95
Or also pretty famous:
Milkshape -
$25
If you think these programs match yours...
It's the programmer's life:
Have a problem, solve the problem, and have a new problem to solve.