That's what the Depreciation does. You depreciate the cost.
IRS overview of Depreciation
http://www.irs.gov/Businesses/Small-Businesses-&-Self-Employed/A-Brief-Overview-of-Depreciation
2018 new IRS info
https://www.irs.gov/newsroom/new-rules-and-limitations-for-depreciation-and-expensing-under-the-tax-...
