You want the longer ones, about an inch long. They will accept two
    separate connections, so you can branch or daisy-chain.

"Three level" is the standard size.

    >how much do wire-wrapping tools cost ?

    The professional wire-wrap guns probably cost USD50-100

And up.

    but you can buy a hand tool for only a few dollars.

About $15, these days.  Get one that does a "modified wrap", if you have a
choice.  (This puts a turn or two of insulation around the post as well as
the normal 7 turns or so of bare wire)

    It's slower and less consistent, but with a little practice, you can do a
    perfectly acceptable job. The other end of the tool is an UN-wrapping tool,
    which you will also need, unless you never make mistakes :-)

And there's a wire stripper in the middle.

    Wire-wrap uses special wire. It's solid, silver-plated 28 ga. wire

30ga. for normal connections.  Still pretty easy to find.

    with kynar insulation. You should get red for Vcc, Black for ground, and
    at least a couple of other colors, as the colors make it easier to trace
    connections when you're troubleshooting.

Multiple colors are nice, especially for debugging.  If you have red,
black, and white, I wouldn't waste red and black on VCC/GND (or not only
there!)

    You should use a special stripping tool which prevents nicking the wire.

Like the one in the middle of the manual tool.  "pro" strippers will run
you another $100...


    It's also possible to buy packets of wire of various lengths, that have
    been prestripped on both ends.

Recomended.  Stripping wires is a pain.

Some things suck with wire wrap, such as memory buses.  If you're doing a
memory array, consider some form of wiring that allows you to daisy chain
connections more easilly.  Passive components are also a pain.  Official
policy was to put them on DIP headers and use normal WW IC sockets.
Assuming that you aren't using a CAD system that generates wire lists, make
a zerox of your schematic and highlight over each segment of a wire run as
you make it..

I spent a summer job after highschool doing prototype wirewrapping, using
electric guns and good strippers.  30 wires/hour (including stripping) was
a pretty good rate for a moderately experienced beginner.  Manual is
slower, of course.  Take your time.  I've actually WWrapped a couple
hobby-sized projects, including an ascii keyboard encoder (ala Lancaster)
and a 6bit 75bps to 8 bit 300bps newswire converter (using UARTs.)  It
works pretty well for things about that size (and probably for most
PIC-style projects.)

For experimenting around, those proto-board things have pretty much
completely replaced wirewrapping.  They're wonderful, and I'm really
glad that they came along right about the same time I started to experiment.
WWrapping is nice for circuits where you're going to build no more than
one or two "production" copies of a device.  There are assorted reasons
why WWraping is reliable enough for production circuitry...

BillW