Hi and welcome to Just Answer!
There are several items you need to consider...
1. My (Wisconsin) parents bought their home in the early 1970's. - the purchase price would constitute the basis.
2. My father passed away in the early 1980's and it became my mother's sole property. - because the property was inherited - your mother had a stepped up basis equals to the fair market value of the property at the time your father passed away. Even she inherited only half of the property - because Wisconsin is a community property state - the total property got a stepped up basis.
3. She did not remarry and it was sold to me (Minnesota) for $1 in the mid - 90's by my mother under life estate. - selling for $1 which is substantially less than its fair market value is treated as gift. Th e gift is not taxable for you as a recipient - but your mother as a donor might be required to file a gift tax return if the FMV is above $10,000. While your mother most likely doesn't owe any gift taxes - still filing the gift tax return could be required. In additional - your basis on the gifted property is the lesser of the fair market value at the time of gifting and the donor's basis.
My mother lived in her Wisconsin house under life estate from that time until she passed in the mid 2000's at which time the home became solely mine. - if the life estate provision was registered in the county where the property was located (normally such provision is mentioned on the title) - your mother was considered as co-owner of the property and part of the property should be included into her estate. If that is correct - the property would be treated as inherited - and you are getting stepped up basis equals to the fair market value of the property at the time your mother died. Otherwise - your basis would be the same as was established at the time of gifting.
I just recently decided to sell. The home is not my primary residence. I married earlier this year.
That is very important to determine your basis as explained above. In additional - the basis should be adjusted by improvements and some other expenses you had while you owned the property.
The gain = (selling price) - (adjusted basis) - (selling expenses).
Because the property was owned more than a year - that will be long term capital gain - taxable at reduced tax rate - not more than 15% (while the rate might go to 20% in 2013). State income taxes are extra.
Please be sure - ask for clarification if needed.
I will address all your concerns.