Telford's ground is closer to Wellington station- but the fares are the same.
If you split at New Street rather than Wolverhampton, then you aren't forced to use LM between BHM and WVH, though the fare is £1.90 more.
In other words,
OPR MKC-BHM (LM Only) £11.50
CDR BHM-WLN £8.70
Total £20.20
This has the advantage in that the LM trains from MKC arrive into BHM at xx:01, whereas the LM trains towards WLN depart at xx:05- so you have a 4 minute dash or a 64 minute wait.
Whereas if you have the flexibility to get any train between BHM and WVH, then there's an Arriva service at xx:24 which stops in fewer places.
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Also...
On the return the LM trains are at xx:01 and Arriva's at xx.45. (give or take a minute or 2 in some hours)
Assuming it's a 3pm kickoff, you won't make the 17:01, so the 17:45 gets you into BHM comfortably in time to catch the 18:53 to Northampton (no direct trains to MKC at that time).
If you wait for the 18:01 (or even change to LM at WVH from the 17:45), then you'll have to get the 19:53.
The extra £1.90 saves 54 minutes on the outward and an hour on the return- I'd say that's worth it!