that 3p-4p cost is applicable to the new large scale wind farms, inclusive of maintenance and decommissioning.
If you knock down an old wind turbine, you can sell the recovered metal. It's not contaminated like a nuclear power station.
Apparently, you can recover the cost of dismantlement by the proceed of recycling the metals.
https://www.windpowermonthly.com/article/961382/cost-decommissioning
Dismantling an aged wind turbine and restoring the surrounding landscape account for between 1-2% of the machine's cost over an expected 20 year lifetime, or about SEK 0.01/kWh (EUR 0.0009/kWh), according to a study carried out for the Swedish energy agency. The study, by market research firm Consortis Producentansvar, will help developers meet requirements that they calculate life cycle costs as part of their permit applications. The Swedish Environmental Court, the final arbiter of permit applications, sometimes also requires financial guarantees for restoration. Dismantling a 2 MW turbine on land and restoring the site is currently estimated to cost about SEK 700,000 (EUR 66,000). Consortis estimates the cost for dismantling a 3 MW offshore turbine at around SEK 1.5 million (EUR 140,000), or between 2-3% of its total costs. Matthias Rapp of industry group Swedish Wind Energy says the sector should now work out a common system for providing the financial guarantees to cover decommissioning that the government demands.