Two Apple ID's for two iPads?

Question

I understand my Apple ID is linked to my apps and their updates and my gift card balance.
I know Apple ID's can't be merged or deleted.
My question is:  If I buy one app, will I need to buy it twice if I want to use the same app on two different iPads?
Does it depend on the developer?
Can I buy the app using one Apple ID and install the app on two iPads? 
I don't want to pay twice.

Answer 1

You absolutely do not need to buy it twice. Read the Terms and Conditions.
When you first acquire App Store Products, as defined below, (excluding products acquired from the Mac App Store) or iBooks Store Products, as defined below, through the App and Book Services (collectively, “Eligible Content”), you may elect to automatically receive (“auto-download”) copies of such Eligible Content on additional compatible iOS Devices and iTunes-authorized computers with compatible software by associating such iOS Devices and computers subject to the association rules below (each, an “Associated Device”). For each Associated Device, you may specify which type of Eligible Content, if any, may be auto-downloaded to it. On an Associated Device that is capable of receiving push notifications (“Push-Enabled”), including iOS Devices, the Eligible Content will auto-download to that Associated Device when it has an Internet connection; on an Associated Device that is not Push-Enabled, including those running on the Windows operating system, Eligible Content will automatically appear in the download queue and you may manually initiate the download within iTunes.
As an accommodation to you, subsequent to acquiring Eligible Content, you may download certain of such previously-purchased Eligible Content onto any Associated Device. Some Eligible Content that you previously purchased may not be available for subsequent download at any given time, and Apple shall have no liability to you in such event. As you may not be able to subsequently download certain previously-purchased Eligible Content, once you download an item of Eligible Content, it is your responsibility not to lose, destroy, or damage it, and you may want to back it up.
Association of Associated Devices is subject to the following terms:
( i ) You may auto-download Eligible Content or download previously-purchased Eligible Content from an Account on up to 10 Associated Devices, provided no more than 5 are iTunes-authorized computers.
( ii ) An Associated Device can be associated with only one Account at any given time.
( iii ) You may switch an Associated Device to a different Account only once every 90 days.
(iv) You may download previously-purchased free content onto an unlimited number of devices while it is free on the App and Book Services, but on no more than 5 iTunes-authorized computers.
The above terms ( i ) to ( iv ) do not apply to App Store Products.
Some pieces of Eligible Content may be large, and significant data charges may result from delivery of such Eligible Content over a data connection.