I used walmart.com in August for a water shipment, and was very peased. I got 2 flats of water - 24 bottles each - for under $9.00. S/H was $0.97 per item, and I think if you order over $40, S/H is free.
I also checked
Amazon for water and the prices were VERY high. I think the cheapest "regular" water could find (not Evian, Fuji, coconut water, etc.) was about twice the price of
Walmart.
Finally, you can get baby wipes, formula, etc. at Amazon but very rarely can you even find single items of something, usually you'll have to order a 6-pack of something. So, if you're going to use a 6-pack of baby formula, it will probably work out well. If not, you'll have a lot of formula to throw away, or try to pack in your suitcase.