I bought my 1 3/4" hole saw at princess auto. It was under $20.

hole saw
 

i have a 2" or a 2 3/8. next size down isa 1 1/2

Princess auto 10 -18 buck each mine has cut about 14 holes already

Since you're widening existing holes, a Dremel tool or something similar with diamond burr bit might work as well. Needless to say, just make sure you've got a source of water for cooling while you're grinding away.

If you are redrilling, my advice would be to predrill a piece of plywood with a 1 3/4" wood bit, clamp that piece of plywood to the front with the hole lined up where you want to drill your new hole. It will give your glass hole saw a guide so your not having it spin off and cracking the glass.

Clamp an undrilled piece of plywood to the back of the glass and dont forget the water running on the hole as your drilling.

1 hole down, 3 to go. Thanks for the help guys!

your quite welcome buddy its more intimidating then it is hard:) goodluck and lets get that badboy built so we can see a fts:):)