A nice pipe should be about the size of the nug in my profile picture. Depending on the quality of the glass you'd expect to spend anywhere from $20-$60
A good traveling bowl would be about 3.5 to 4 inches which usually costs 10-15$ if you want a reliable bowl that you want to use every day I would get a 4-5 inch bowl which should only be around 15$
Definitely depends on what your using it for. going out id say 3.5-4 and as thick glass as you can get, may cost a little more but you'll save yourself the headache of a cheap thin one breaking in your pocket or backpack or what not. but for home the sky's the limit a shorter bowl usually has a smaller physical bowl to pack herb in so depending on how much you smoke at a time could help influence overall bowl size
I'd say 4 or 5 inch, so you don't burn your nose or eye lashes/brow. I wouldn't pay more than 15 bucks for a glass pipe, unless it's a worked piece.