In my opinion,
To overcome expensive DD consultants costs; DD can be structured in many phases or steps. First part is analyzing overall generic data that can be done in-house utilizing the available capabilities. Then, moving to more detailed DD that rely on one overall DD consultant. Finally, in depth DD phase which of course will involve other depth scope oriented consultants.
Following above DD structure will ensure that buyer will only pay what is needed (Cost Control). Also, it will provide a smooth DD process with buyer as not all books are opened in early phases of the DD.