The Crimson Falling
As per house rules, Parry comes as a trained basic skill (ie. you roll full WS to parry).
You can purchase/upgrade Parry alongside Dodge, starting from Dodge +10, at the same price.
If at level 1, you can purchase Dodge with 100xp, go ahead. You already have Parry, trained.
If at level 3, you can purchase Dodge +10 with 100xp, you can also purchase Parry +10 with 100xp.
If at level 5, you can purchase Dodge +20 with 100xp, you can also purchase Parry +20 with 100xp, if you’ve got the prereq (Parry +10, of course).
The cost of dodge and parry will always be the same (100 = 100, 200 = 200 etc.) and the bonus training will always be available at the same level, for both.