We have bought all of our vehicles here in DR for the last 16 years. Initially because we heard the horror stories (e.g. US$15,000 tax at Customs) and more recently because we were told when an expat mechanic who had
really looked after his jeepeta was leaving the DR & needed cash.
Overall, I strenuously avoid putting myself in any position where I am open to getting the run around - just takes up too much time and is hassle. I don't have an 'in' to Customs although if I really needed one I know how I would work at it. But that's just it, too much 'work' and I prefer to spend my time doing the things I enjoy doing.
I'm somewhat amazed at the US$300 to get the car out of Customs. There was a US$15,000 one about 4 years ago (ok he was obnoxious & Customs made him pay for it

). But let's ask people who have brought their cars in, how much they paid in taxes & then we'll get a broader picture.