Yes, you can adopt the standards for part of an organization when you define the scope of your QMS. The decision about the scope is a management decision, not a technical decision. For example, a manufacturing organization can decide to certify the part of the business that works for B2B and leave out of the QMS the part that works for B2C.
Also do you have any info on costs for purchasing the accreditation?
The correct word is certification. You cannot buy the certification directly. You choose a certification body and that organization, an independent third party, will audit your organization through a set of audits. A first one, called 1st stage audit, will audit the overall design of the management system and documentation. After passing that first stage there will be a 2nd stage audit. This one will audit the whole organization under the scope of the management system, auditors will check implementation, interview employees, observe operations and locations. After passing this 2nd stage audit the certification body will issue a certificate declaring that your organization has a management system operating according to the reference standard (for example, ISO 9001 for a quality management system).
The cost of the certification process will depend on the number of days of the audit. The main criteria for determining that the number of days will depend on the number of employees of the organization. Certification is like any other business, some certification bodies are more expensive than others due to brand recognition, for example.