it is one of the most importnat requirement of todays online business . It provides trust and faith to your customers.
I run a few ecommerce sites and if you want to have secure checkout and use a payment processing company like Authorize.net then you will need an SSL. You can get them for 12.99 through godaddy. Do a search on google for ssl certificates and their coupon will pop up. Otherwise your going to pay around $50. Good luck!
Yes it is recommended for any login pages or pages involved with submitting sensitive information. It's definitely worth the price and honestly visitors are so savvy now that some of them actually check to see if you have a secure submission page before bothering to join.