Hull (HUL) - Coventry (COV)
Anytime Return (SOR) via Any Permitted route is £
116.00 (ouch!)
Off Peak Return (SVR) via Any Permitted route is £62.90 but not valid until 0930!
For starters, a ticket to somewhere like Basingstoke (BSK), route Not London, is priced at £
97.80 for an Off Peak ticket but this ticket is valid from 0500, so would get you to Coventry for 0930. You could then finish "short" at Coventry, and start "short" at Coventry on your return. So, with one ticket, you can save just under £20.
However it's probably better to split the journey into a combination of tickets. It is difficult for anyone to come up with a combination and say "this is the cheapest", all anyone can do is come up with a reasonable combination and see if anything obvious is better, and if not, go for it!
The usual places along the CrossCountry route are places like Sheffield, Derby, Birmingham, but it can vary.
Hull - Sheffield
Anytime Day Return (SDR) £22.50
Sheffield - Derby
Anytime Day Return (SDR) £17.20
Derby - Coventry
Anytime Day Return (SDR) £15.50
Total = £55.20 return
Saving around £61
(We should charge for this!!

)
This was just a quick search, so may not be the best.
Note that the train must call at any station where you change from one ticket to the next
(unless they are zonal tickets or you have a season ticket - this doesn't appear to apply here)
The railways penalise customers who do long journeys (unless they are really long, as with the Basingstoke example).