What type of journey from Plymouth to Exeter in 1751 might cost 1 pound 5 shillings?

Question

My 6th great-grandfather Robert Osment was baptised on 8 Mar 1703, married (to Elizabeth Simons) on 3 Jan 1729, and buried on 6 May 1756, with these life events all occurring at Plymouth Charles, Devon, England.

In the Devon, Plymouth Borough records 1519-1905 at FindMyPast there is a very clear image in the Borough Receivers' Accounts that says the amount of 1 pound 5 shillings was:

Paid Robert Osment for a Journey to Exeter

The entry is undated but it is near the end of a long list of such entries for Charges and Disbursements from 29 Sep 1750 to 29 Sep 1751. FindMyPast dated the event as being in 1750 (see below) but I suspect that it was probably around Aug-Sep 1751.

Given the wording and amount paid, can anything be inferred about the type of journey (from Plymouth to Exeter) that may have been paid for and thus the likely occupation of Robert Osment?

Event type  Borough Receivers' Accounts
Record set  Devon, Plymouth Borough Records 1519-1905
First name(s)   Robert
Last name   Osmont
Event year  1750
County  Devon
Country England
Place   Plymouth
Years   1739-1784
Archive Plymouth & West Devon Record Office
Archive reference   1/134
Category    Census, land & surveys
Subcategory Courts & legal
Collections from    England, Great Britain

Answer 1

In "The Transport Revolution in Industrializing Britain: A Survey" (pdf) by Dan Bogard at UC Irvine, a table on page 14 gives Stagecoach Fares in shillings per passenger mile, with a value of 0.23 in 1760, which is reasonably close to 1751.

On Google Maps, Plymouth to Exeter is around 45 miles by current roads, but that could be somewhat higher using 1750s "roads". If we say 50 miles travelled, that gives a cost of a return journey of 50 x 0.23 x 2 = 23 shillings, or one pound three shillings. That's very close to the quoted 25 shillings cost, so the cost is consistent with a stagecoach return journey if no other substantial costs were involved.

At an average of 2.6 miles per hour, each way's travel would have taken around 20 hours, so would have been split over at least two days.

This doesn't exclude other transport options of similar or lower cost, of course. Robert could have gone alone on horseback (probably cheaper, but perhaps with added danger from highwaymen!), or even gone by sea, although that's not a straight route.

And it doesn't help with why he went. He may have been a passenger taking something to Exeter, or meeting someone there, or bringing something back. Or he may have been the carrier/driver, who charged the borough for taking someone to Exeter. (Purely speculatively, Plymouth is within the diocese of Exeter, so taking someone/something to the Bishop of Exeter could have been a valid reason for such a chargeable trip.)

Is there anything on Robert's burial record or the baptism records of his children that refers to his occupation?