You can't get a 4x4? That's about the only thing they rent out there! We wound up with a Chevy Equinox a couple of weeks ago. It was AWD, wasn't sure if it had the required snow tires, but Budget insisted it did (aren't they supposed to have the red dot on the side, so CALTRANS can easily check them out?)
Anyway, given that you really can't get a 4x4 -- as opposed to not being able to afford one!
-- just remember that a lot of it depends upon where you're staying and what your plans are. If you're staying on Tahoe City, they'll close 89 on Emerald Bay for just about anything. Once you drive it, you'll know why. Which means, a 40 minute trip to South Lake will turn into an hour and a half as you round the lake over the top. The Carson Pass doesn't close as quickly, I think because at least they have guardrails! But it it snows hard at Kirkwood, you won't get out anyway, and won't want to.
More important, I'd talk to the rental company. On a previous trip we asked about putting chains on our rental and they said our rental agreement strictly prohibited it, and they'd charge us a buttload of money if there was evidence chains were installed on the car, especially if they broke and caused damage. Don't know how often this happens or is enforced, but it's worth checking into.