Shipping has never been much for me. I belive they do it by the dollar amount you order. I don't like makeing an order for just a single or few items, so I try and wait till I can make it worth my time doing so.
No, a heater will only heat the water. A chiller is what you would need to lower the temp of the water. If you think any heater you've ever seen was expensive, check out the chillers.