Best I have come up with ... but I do not know what balance between fare, timing and number and ease of changes is.
Outbound journey:Melksham to Gloucester -
07:21 to 08:45
Gloucester to Nottingham - 09:49 to 12:04
Nottinghham to
Boston - 12:45 to
14:17Possible an hour quicker, but adds change at Birmingham New Street and fare total will be higherMelksham to Gloucester - anytime day single - £30.30
Gloucester to Boston - off peak return £100.20
Glouceter to Melksham - off day peak single £15.90
Total - £146.40. Add senior railcard - 34% + £30 =
£126.60 return or £96.60 if you already have railcard
Alternative routing: for earliest arrival (around 12:15)
Melksham - Swindon - Paddington - Kings Cross - Grantham - Boston
Errors and Omissions Excepted
Return - included in fares above within 1 month
2-change option is 12:50 from Boston, 14:19 - 15:07 at Nottingham, 17:27 - 17:50 at Gloucester, 19:09 into Melksham.
4-chage off peak option - 09:54 to 15:39, add Derby and Swindon changes