Decompilers are part of specific IDA subscription bundles and cannot be purchased separately. Depending on the plan, you can get 2 cloud-based decompilers or two, four, six, or all local decompilers. If you want more decompilers than your plan offers, upgrade to a higher plan. For instance, if you opt for the Expert-2 plan with two decompilers and later decide you need a third one, you would need to upgrade to the Expert-4 plan.