As someone else mentioned, we ideally need more info and/or pics on the car to answer completely. Just saying where you are would be a start. Big difference between a car that has sat for 10 years in the southwest, for example, versus the northeast. Even saying that, next question is sitting where, on asphalt or grass?
That said, I have purchased several old Mercedes that sat for far less time, maybe 4-5 years. I have seen those cars eat $800-1500 in parts within months. Fact is that, excepting cases of chronic illness, loss of driving privileges or an estate issue, good running cars generally don't get left somewhere for 10 years. The car probably had issues when it was parked, so you will be faced with identifying and correcting those before you can address the stuff that is gone from sitting.
If by rusty you mean it has visible rust, then honestly I think you are sunk. These cars rot in visible places last (excepting stone chips that have been left to rust out). Once you have fender rot, etc., you can be guaranteed a good chunk of the underside is soft or gone.
You say it has 135k miles but is that documented or confirmed? The odometers on these old cars commonly break. If it is 135k miles then it would be a shame if it was abandoned and left to rot, but it happens.
It is highly unlikely that you can make it a viable proposition
for the long term for less than it would cost to just buy a relatively solid, running example. Don't ask me how many times it took for me to learn that.
