One of my retirement goals is to redo my math degree - turns out it's really easy to get hooked up with online tutors, and I figure it's totally worth paying $20-$40 an hour to work through a textbook.
All you need is updated texts, a plan of action, and maybe Wikipedia for an alternate take on sticking points. (Just using Wikipedia doesn't work well.)
You could also look at the MIT or Harvard online curricula/syllabuses to get a feel for what the current subjects and texts are. Maybe take a couple of the free courses.
Also, scan Kahn Academy first - that site is good for identifying holes in your background.