Can you give me an approximate Idea of costs for.

Costing is something that we are not able to help much because they can vary by a lot depending on where you are located.
Parts, lubricants (brand and quality makes a lot of differences) and labor cost could vary vastly so the difference might run into hundreds. To have an accurate estimate, it is best to enquire locally and also depends on the term Service B as different shop might have a different understanding of the services required.

Spark plug replacement might not be required as it depends on previous services.

There are normal and platinium plugs that varies by up to 400 % in cost difference.

After more than 30 years in the industry I still find that people do not have a common understand of standard services and what needs to be done, even at dealers but prices for dealers would be constant as they are linked.

Severe or normal usage, driving and weather conditions makes a difference to interpretation of services as well.

Services in our database indicates that services are for 50, 60, 100 and 120 k miles and does not have any indication what is A or B service.

Whatever price I give you might be vastly different from what you are going to get and the best place to check would be the one you are going to send the vehicle to. You can try a few shops locally and compare the difference.

This is one of the reason I was not willing to provide any costing.
When a vehicle is at a certain age, there are bound to be additional work on normal maintenance services.
For normal services, the things listed according to the work sheet are what the shop should go through and the cost can be upfront but if any of the inspection list components are found to be bad or failing, the shop should let you know and get your approval for replacement. This can run into additional amounts that can be up to hundreds.

What you need to find out is what are the additional work recommended. If it is something that is already bad, you have no choice but to have it replaced. If it is something that is not important, is not bad yet and won't affect safety, maybe you can defer the repair.