If you are asking for the cheapest combination of tickets, where journey time does not matter, then my answer has to be that no-one has yet devised a program that can calculate that (and I would be very impressed if anyone does!) therefore all you can do is do individual searches and figure out the best compromise for you, between cost and convenience.
"Splitting" the journey into a combination of tickets may work. I find the easiest way to do this is (other than to use Avantix Traveller) is to use a WebTIS website (e.g.
EC,
LM etc) and click the info (i) button next to the itinerary you want, then tick 'show all calling points', this shows the places where you could "split" the journey into a combination of tickets (note the train must call on the return journey too). Examples here include Crewe, Stafford, Wolverhampton, Shrewsbury...
Note that if you want to return a different day (as in this case), it will not be cheaper to split at stations where only
Day Return tickets are available. Therefore, it is
generally only best to look at longer distance tickets, where (Super) Off Peak Return (SSR/SVR) fares can be combined, but that does severely restrict your choices, especially if you choose a station that not all trains call at (such as any of the stations on the Berks & Hants route or the Honiton route).