Welcome to SF and Tahoe. Good store in around Tahoe is Porters Tahoe, stuff would be on sale at this time, and they price match, maybe try looking ahead of time, get the website, ask them if they have it at the store around where you're going, if they will price match it.
Second thrift store search. Burlingame Coat Factory in SF. Craigslist SF Bay Area if you don't mind going around.
Some resorts may also rent out soft goods.