If the owner does not obtain the permit required by sections 7.290 to 7.308 within 20 days after the date of the notice or does not do the necessary repair or reconstruction as authorized by section 7.153 within 20 days after receiving the permit, the city engineer may cause the repair or reconstruction to be performed either with city forces or by private contract. If the work is performed by city forces, the owner shall be charged at a rate established by the city manager pursuant to section 2.020 of this code which shall cover the costs of the work, including supervision, inspection, billing, overhead, and whatever additional costs any extraordinary aspect of the work entails. If the work is performed under private contract, the owner shall be charged the amount actually paid to the contractor, plus a charge for supervision, inspection, billing, interest on warrants and overhead, as established by the city manager pursuant to section 2.020 of this code. The finance officer may collect the cost of the work plus interest thereon as provided in section 2.022 of this code from the owner, or proceed, in accordance with section 6.100 to cause the cost of the repair or reconstruction to be assessed against the property, and made subject to interest and to lien and foreclosure. Payment of the lien may be deferred, extended or modified as provided in section 7.195.