The SDK is only available for purchase separately and I'm not sure it's even sold anymore. However I integrate with MAS 500 in a wide variety of ways and do not use the SDK for that. If you tell us what you want to do maybe we can help you.
The SDK is available for sale. Depending on what module(s) you are using and what screens you want to integratee to will determine what you need to purchase. Also, you do have access to the database without purchasing the SDK. Just be aware, that we cannot support modifications you make to the application.
Have you talked to your partner about what you are trying to achieve?
Good luck,
Darrick
First are you looking only to query data from the 500 database or are you also thinking of creating/modifying records? Also, what type of program are you looking to build (i.e. client that works within Sage 500 session, interface to another system, retrieve data for a website/web service, etc.)?
Depending on what data you want to look at, you can likely find what you are looking for in the BIE views. For example, if you go to Sales Order - Insights - Explore - Sales Order Lines, that BIE view uses the view vdvSalesOrderLine, which can been seen by clicking on File - Properties for that view.