i have been making plenty of homemade bongs for a few weeks now, this is what i would suggest
dremel tool
diamond drill bit
go to your local headshop get some downstems like so
http://www.bolinat.com/product_max.asp?id=2226
then get the male to female so you can obviously have a slide in it...
get some gorments to seal it airtight
http://www.bolinat.com/product_max.asp?id=3644
or like the guy above said "HOT GLUE GUN"
when making my first one i found that "MIGHTY PUTTY" works to great...its a bonding agent that bongs onto to everything and anything...you might have seen it on the late night infocommercials...
anyways u get your dremel tool...make sure to either have someone with a spray bottle (the one used for hair/windex) and continuesly spraying the glass itself...its not nesscary but it helps from the glass cracking, and otherwise u wasting the past 20 mins of your time lol
another thing someone told me was submerge the entire bottle in a sink, or a tub of some sort to once again keep the glass from getting to hot, and chipping...i found it was a bit hard to cut, due to the fact that water plays tricks on your vision...
anyways drill the hole...or "cut it out" like said above...
try to "soften" the edges a bit so there not razor sharp lol
you can also use your dremel tool to make a few diffuser holes on the downstem as well...your choice not needed...
stick the gorment on the downstem/male/female stems and wala your good to go =]
no need for a carb really if you wanna make it slide....your prefrence really
all together to make and get everything will probably be about 75$....dremel tool being about 45.00 depending
you can go to your local friendly walmart and they have the dremel tool there for you for about 45-65 depending on the set you get, more adapters and such
another thing i found that worked very very well, is pour spouts.
every bar that you go to has a pour spout...its what controls how much alchol you put into your drink...anyways it has a seal tight...SEAL...lol that keeps the liquid from leaking out (obviously) most bars will let u keep them, cause there a one time use.
take out the pour spot,whether its plastic or metal...pull the piece our and wala...you now have a perfect "drilled" hole, that you can use for whatever make-shift bong your heart desires to create lol
anyways hope this helps....message me if you need any help, as well as seeing some of my bong creations
hit up your friendly good will store, get some vases or whatever and make something beautiful =]