Post #3 here and the link to the adjustable bed thread should be helpful and includes several sources that you can use as a “value comparison” for the most common manufacturers and models.
I would always treat a mattress and an adjustable bed as separate purchases unless the retailer or manufacturer where you are buying a “combination” has the mattress and the adjustable that you would otherwise choose based on their own merits and the price for the combination is better than purchasing both of them separately.