If you are a member of BJs wholesale club, go to their website and use their travel link for rental cars. you can get a good discount code. I have used rentalcarmomma.com and got great discounts.
Getting the best price takes lots of work. I usually plug my dates into all the major rental companies with every different code I can find and try to work the best deal. And just when I think I have a great deal, I recheck all the sites (with codes) a few weeks before we leave. I almost always get an even better deal. I've also been told you can use coupon codes with the corporate codes- I've never tried it. But I'm gonna with the next rental. (example- coupons in entertainment books)
Good luck- the work is worth the discounts.