2004 Ford Taurus Car would not start after driving to and f

Car would not turn over. Called AAA, Battery Assit came and replaced battery. I did see that the posts had corrossion and a liquid on top of battery. Bought car from my former employer, pretty sure it was original. After trying 3 times to start car, it did. The guy from AAA said it was the starter. I took it to my mechanic, they said it was the starter and gave me a price of $300. Took them until the next day (I have been going to them for over 10 years with 4 different cars). A co-worker said her husband bought a starter for his truck and the cost was $20.00 for the part. So did my station snooker me? The tech writer also said there were about $1000.00 repairs I needed to do. One problem 1 motor mount, did not say which one. Hoses, transmission leak-gasket, and other problems/ I live on soc. Sec. Just now without working, I really don't have money in budget to donate. I am sorry. Being an older woman I would like a response please.