As per house rules, Parry comes as a basic skill. Its level of availability is always matched to the level of availability for your character.
If Dodge is a starting skill, you now have the choice between Dodge OR Parry
If at level 1, you can purchase Dodge with 100xp, you can also purchase Parry with 100xp.
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.
All prerequisites still apply (Dodge +10 requires Dodge, Parry +10 requires Parry, etc).
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.