Hmm, I can't recall the last time I used turn signals off-road and if I ever do, I'm doubting I'd impress the guy behind me by having them sequence in 10 steps instead of 3.
Regardless given the limited market for that, it doesn't surprise me that it comes at a price premium.
I noticed your
EEVBlog post where you mentioned that you found 9V modules.
You could try using one of those, regulate the (presumably) ~ 14.4V vehicle electrical system voltage down to 9V to drive the module, then use the 10 outputs which would drive the lights, to activate relays for each 12V automotive bulb, to give them 12V (probably closer to 14.4V running) from a fused vehicle battery lead, like the original tail light circuit.
When it's all said and done, considering you're starting out in electronics and will have to fabricate a weatherproof enclosure for this and measure and test, etc, $130 could be your best bet for something ready made.
