I am new to traveling, so I don't have experience with Nursechoice. However, what you are describing sounds way too vague for you to consider accepting. They might be talking about the Tax Advantage program-where a certain amount of your pay is untaxed. You really need to send your recruiter an email and have them reply with EXACTLY what your compensation will be. I would say that you already have seen a big red flag in that you aren't certain of what your pay really would be. And this is before you have seen a contract?
On my first travel assignment I was really taken advantage of & have since studied and learned a lot in order to not make the same mistake a second time. Depending on where you are going your base compensation should be around $30.00/hour, including fully furnished private housing (with the houseware package) and insurance. After you have determinied the real base rate of pay, then you can talk about the other amount & what is going to be taxed and untaxed. If they are going to put the rental car in their name and pay for it direct, then expect to get a deduction from either the hourly rate or a weekly amount; but, add it up to see if they are taking too much. You have to tell your recruiter to spell it out down to the penny or you will walk. There are a lot of good companies out there and you can find the very same job through one of them. At this point in your dealings with a company, you should not be so confused on what you are going to be receiving in terms of your weekly pay!