Hello Rex and a warm welcome to the forum !
There's really no such thing as a standard car, it starts I suppose with the base spec on which you can then add on a large number of options depending on your budget and the use you intend to use the car for ..
There's an Excel macro-enabled configurator spreadsheet that lists them all along with the costs - note that these are at build costs and some options will have an additional cost if fitted post-build.
I guess you've seen the Ariel website which explains most of these but omits the costs?
I've only got a copy of the configurator from 2013, I've shown the 2 roll bar options from that below.
Middle column is the dreaded VAT.
The bolt-in option does just that - the holes are already pre-drilled.
The welded option will not be so easy to retro fit as the heat will affect the powder coat chassis etc.
You could always contact the factory about this ..
Other than the Atom Cup race-spec cars (now disbanded) I don't think many cars have this option (nor the bolt-in one for that matter!)
Should you have any other queries, someone on here will know the answer
Bolted in Full Roll-Over Bar - Road/Track Day Use £600.00 £120.00 £720.00
Welded in Full Roll Cage MSA Approved - Race Use £987.00 £197.40 £1,184.40
John