reflash will only woork if it's a V7 or newer.
STM work is quite expensive, but very reliable I'm sure. Their re-flash rates are $1250ish (as advertised in their thread here), as opposed to Speed Source up north who will do the same for about $800ish, but they are opposite sides of country, so it really depends on what area you live in.
If you wanted to check out other places, I'd send Speed Source an email, a figure of what you are wanting, and see what they can offer. But only if you can afford to take a week or two off work and stay in Whangarei while they work on your car.