When I was comparing the regular Altima vs the HEV, I did a comparison of costs, taking into account the price I can purchase each car, fuel price, interests, etc...

The hybrid with a reasonable discount was $32,743 and $28,685 for the 2.5SL.

After the $2,350 tax credit, averaging 14,000 miles a year X $2.81 /gallon, After 4 years, the hybrid will have cost me $540 more, 5 years, $183 more, 6 years, I would be saving $172.27

There are other things you need to consider too when comparing the Altima. The 2.5SL does not have Traction control or stability control options, but the Hybrid has them standard. I think I will have received my value within 4-5 years in this case