Is there any accounting software plugin available off-the shelf with minimal customisation?

Hi everyone in this community, please bear with me as I’m new here. One of my clients who is a bookkeeper approached us to create an accounting software for the automotive industry, and I’m wondering if anyone is aware of an off-the shelf solution that can be customised within a few days, an that is flexible enough to fit our potential client’s requirements. An example of this is Ember, or CarVue, that our client said they’d like to have a combination of. Any advice on this would be much appreciated, or any guidance on how I could serve the client with the least budget would be great. Many thanks.