Total costs for the IMO was quoted and paid at $1500.00; nothing else was asked for at all and it seems like they do this often on the side. This cost for IMO was also true for Dr. Bash. I had a few other quotes in the realm of $3k-5k dollars. Honestly, this it what I would expect from a medical expert. When I was working with attorneys, expert witnesses were almost $1500 a day, and about 2k-5k dollars to write a report for the case.
My reasoning in getting the IMO was that after having the VA look at the wrong records (cited as 13 years before my birth), denying all my claims except one, and not performing any of the required tests - I felt that my best option was to have an IMO. For a total cost of $3,000, I may or may not have been able provide all the required evidence to prove my claims; I think my claim is also simple (OSA). For others, where their claim is more difficult, more disabling, or far more intricate, I think an IMO could be a blessing. I was also very fortunate that this wasn't going to put me in a bind financially (Used GI bill $ from school to fund it).
My biggest suggestion: Put as much evidence as you can into it. Submit lay statements, submit medical journal's in support of your claim, try to find a Dr. to submit a nexus letter, go to the VA and get treatment etc. Do whatever, legally, to tip the scale in your favor.