If you are really getting $0.98/mile then drive what you like. Figure out what you are spending for the MGM and save the rest for another car or replacement.
Figure 20 MPG for mixed driving for the initial estimate, and at $3/gallon for gas you are looking at $0.15/mile for fuel at that price.
Add half that again for maintenance and repair.
Just looking at my $10k 2012 Mazda3 I bought 4 years ago, and the purchase of my car is still the biggest cost at $10k, fuel has been $5680 and repairs and maintenance have been $1812. My total cost per mile over 70k+ miles has been $0.24/mile (Purchases at 68,8xx and today it has 141,0xx miles on it.
If you are really getting $0.98/mile, you should be able save half or more of that even at $0.20/mile as your operating costs will be on the order of $0.22/mile not counting the cost of the car or your insurance.
You are talking about close to $70k in reimbursements over that 70k miles, like $68k plus. You are going to spend about a quarter of that in operating costs, leaving you around $50k in your car kitty to get something.
If it were me, I'd have a car account where all the mileage reimbursement goes and the operating costs come out of it. At the end of a year, I'd evaluate and see what I could do with the money I'd accumulated.
You could probably buy one nice new car, or a fleet of dream hoopties. Or buy some $20k run-about and bank the other $30k for some other purpose, etc.
The $0.98/mile seems high, unless that's both your wage AND your mileage. If it's both, then taxes come out and it's a very different ball game here. If that's the case, you keep records and deduct your work mileage.