Just a lab to test something regarding OSPF cost.
When I was trying that, I discovered that cost is only applied in inbound direction.
I made a sample LAB to test that :

Loopack 0 on R1 is part of area 0. Path cost is changed on fa 0/0 on R2. If you tried to configure it on fa 0/0, the cost is not applied to R4.
Result :
R4#sho ip osp da summ 1.1.1.1
OSPF Router with ID (4.4.4.4) (Process ID 1)
Summary Net Link States (Area 1)
[…]
LS Type: Summary Links(Network)
Link State ID: 1.1.1.1 (summary Network Number)
[…]
TOS: 0 Metric: 101
Summary Net Link States (Area 2)
[…]
Link State ID: 1.1.1.1 (summary Network Number)
[…]
TOS: 0 Metric: 2