My general view is that the Grail Reliquae is strong and cheap.
Is it too strong? I don't think so.
Is it to cheap? It well might be.
It makes use of otherwise nearly useless peasants (The only use I can think of in WMR is as a support for bowmen, which do not fit in any of my tactics well,) by making a highly usable brigade of them.
Is it wrong? I don't think so.
Without the reliquae, the only infantry option would be men-at-arms. And as the relative strength of cavalry (knights) to infantry shifted in favor of the infantry, I see it good that Bretonnians have a highly usable infantry unit in their arsenal.
Back to "is it too strong?"
It is not an immortal unit. They do not have any armour save and die rather quickly. (It is important to note that if you protect the reliquae unit itself, you can bring fresh peasant units from the reserves to step up for the wounded/killed ones.)
They have another weakness which can be exploited - they have to charge on initiative. Which has also been altered by WMR rules (as the reliquae unit can do the supporting charge). By cleverly placing units in 20cm range from the pilgrims, the whole brigade can be easily divided into two parts (with only 1 unit of 3 remaining in touch with the reliquae unit).
Back to "is it too cheap?"
Especially in smaller games such as 1000 points, its strengths stand out even more if they're used properly. And as a meat shield against shooting - if played correctly, it's simply too many of them to get rid of them effectively before the other bretonnians get at you. But Skaven have a meat shield too (on the other hand, they are much harder to handle if you want them to move fast forward.)
Increasing their cost to somewhere between 40 and 60 would, in my opinion, balance it rather properly.
Another option which I'd raise is to change their "immune to terror"rule to be an activated ability instead of being a persistent one. However, as Aldhick pointed out in one of our discussions, it does only affect the balance against some specific units and armies.