The cost base is usually what you paid for them, plus capital costs incurred (eg brokerage on the purchase and sale).
For example, if 1000 shares were bought for $2 each, and the brokerage on the purchase was $50, and then they were sold for $21 more than a year later (brokerage on sale also $50), then the cost base is
1000 x $2.00 (= $2000) + $50 + $50 = $2100.
The sale price is $21,000, so the capital gain is $21,000 - $2100 = $18,900.
Since the shares have been held for more than 1 year, then the CGT discount applies, and the taxable capital gain is then $18,900 / 2 = $9450.
In some cases, there may be a 'capital return' - which is a bit like a dividend (ie you get a cheque) - but the capital return reduces your cost base. I don't know if this happened with Woolies shares. But I expect that someone will post details for you.
Also, did you participate in the DRP? (dividend reinvestment plan). If you received a dividend (cheque or direct payment to your bank account) every six months or so then you probably didn't participate in the DRP.
If you did the DRP, your capital gains calculation will be slightly more complicated, since there will be a small parcel of shares that you will have received within the last 12 months, and the prices paid for various parcels of share will differ.
Finally, since the shares were purchased (in your case
transferred) before 1999, there is a second method for calculating capital gain, called the 'indexation' or 'index' method. I don't think this will be beneficial to you. But if you post the details of the shares, including the date of transfer to you husband, and if you were in the DRP, someone will be able to work it out for you.
Finally there are two very important documents for you to read and understand, you can download them from the ATO at
Australian Taxation Office Homepage
NAT2632-06 You and Your Shares.pdf
and
NAT 4152-06 Personal investors guide to capital gains tax 2005-6.pdf