I travel once a month. I am good at this now.
Get a baseline on carrentals.com
See which companies are offering deals.
Then go to the flyertalk forum in the car rental section, and see if there are any codes that you can use to get the price down.
Be careful, some codes are for employees of certain companies only, and you will get to the counter and they will want ID documenting that you work there.
Others are good for everyone.
Also double check with hotwire rates.
Then look at better bidding, and see what people have scored on priceline doing the car rental bid thing.
Yes, I have rented standard cars in Los Angeles for 9 dollars per day. Same deal with Vegas.
Don't know about Boston, never rented there.
I know that in Phoenix, they have the highest taxes on rental cars in the nation. The trick there is to take a cab to an off airport location, and rent there, then return the car at the airport.
I have saved 200 bucks a week taking a 5 minute cab ride from Sky Harbor.
For my next trip, Buffalo, New York I have to rent at the airport. I still scored 68 dollars all taxes included for 3 days. Economy car.
I buy primary coverage insurance from American Express for $19.99 for the whole trip, on every trip.
Don't pay 15 dollars per day for insurance, and don't use your own car insurance, unless you want to pay full deducible and loss of use if anything happens.
20 bucks to Amex for primary insurance is worth it.