How long is this going to take?

There is no substitute for good planning - and it often takes time.
Using Web 2.0 applications with a project based learning approach can lower your overall time spent planning.*
Many Web 2.0 apps are modeled off of things that you already know how to use (Office suites, drawing, pictures).
You don't have to learn the ins and outs of an application to use it, your students will learn a lot by experimenting. Let them teach you.

How much is it going cost?

If you have a computer (made in 2003 or later) and an internet connection, you can do most of the things discussed on this site.
See the "Equipment" section for a number of tools under $25 that will enhance the classroom experience.
Beg, Borrow, Plead - Find people who are moving on or upgrading (businesses, neighbors, colleges) and get it low cost or free.
Pressure administration to use technology dollars on computers and projectors, NOT software or interactive white boards.
There are technology grants galore, I've acquired all my tools/toys through grants. Write one grant and send it all over.

If you create an edublog, you can monitor and approve everything that comes through - you are the gatekeeper.
Many web 2.0 apps have education editions that offer teachers free access and privacy options.
While most apps teachers might use are probably safe, your best bet is always to preview it beforehand.