Where do I add an asset's purchase price?

Add the cost to purchase an asset.

The purchase price is the amount that was paid to buy the asset.

Are you setting up a new asset?

Yes, I'm setting up a new asset. Use the field titled Purchase Price on the Depreciation tab in Setup New Assets. Enter the cost of purchasing a single asset. See the help topic titled How do I add an asset?
No, I'm updating an existing asset. Use the routine titled Enter Manual Transactions to record the asset's purchase price. See the help topic titled How do I enter manual transactions?