Check if this could be a solution for you
1. Use your MSDN subscription and build an on-premise instance for dev purpose.
2. Use the non-production instance of your CRM online subscription as a test environment. You get a non-prod instance if your subscription has more than 25 professional licenses. You can choose to use this for dev if you don't need a test environment separately
(additional instance will then cost you 150$/month).
While you can use the trial version for a quick check. It will not be of good use for an implementation.
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