Custom Build or Your Existing WordPress Theme?
If you're starting from scratch
A custom build means the design is made around your brand from the first page - no template stretched to fit a taxi business, no unused sections left over from a generic theme.
If you already have a WordPress site you like
The booking system and quote calculator can be added directly into your existing theme. You keep the design, branding, and any content you've already built - the booking flow and admin panel work the same either way underneath.
Which one costs more?
Neither option changes what's included in the admin panel or pricing engine - see Pricing for the license options. The difference is only in how much of the front-end design work is needed.