An off-peak day return to Mills Hill Manchester (MIH) costing 7.40 should cover what you need and could be the cheapest way of doing this flexibly ( valid by the shortest route +3m rule to Burnley then Todmorden and then via Manchester Victoria,Salford Crescent, Bolton.)
http://www.brfares.com/#faredetail?orig=BBN&dest=MIH&rlc=TST&tkt=CDR
That has the constraint that you'd need to use services stopping at MIH.
Unfortunately, I think the only mapped routes that include journeys over the Todmorden chord currently only facilitate East-West journeys between Burnley and Hebden Bridge so they're not useful for your proposed journey.
£7.40 is also the Any Permitted CDR for BBN-MCV. The VIA BROMLEY CROSS ticket at £7.15 plus a 15p excess would save 10p, but is it worth the hassle?
That's true but neither of the Blackburn-Manchester Victoria off-peak day return tickets would be valid via the Todmorden curve, would they?
Direct train rule?
The ANY PERMITTED is surely valid via TOD even without the direct train rule?That's true but neither of the Blackburn-Manchester Victoria off-peak day return tickets would be valid via the Todmorden curve, would they?
....
oh dear - except via the direct train rule - as pointed out below. (I'd only looked at the fastest journeys and hadn't realized there are plenty of direct trains via Todmorden.)
I think you're right - MCV could be the best option as a destination for the OP.
The ANY PERMITTED is surely valid via TOD even without the direct train rule?