The amount is on the recorded lien. Look at it. Have a title company fax you the document.
IRS does not often redeem a property that has gone to tax sale, I believe. However, given the way properties sell at tax sales in CA these days, that is probably ok for the IRS. Probably the price will be bid up enough to pay their lien plus the taxes owed.
We are considering going to a tax sale in CA and one property that we did a search on shows a Federal Tax Lien from 1996. How do I find out how much it is for? Does the IRS usually redeem a lien on an auctioned property after that length of time? They had another one in 1991, but that shows up as released.