Can a mechanics lien be filed in Maine by out of state law firms and at what cost?

 If you are talking about only filing the statement required by 10 M.R.S. § 3253 with the York County Registry of Deeds, depending on how complex it is to prepare that statement, it should likely cost between approximately $1,000 and $1,500. No, the statement cannot be completed online but, once it is properly prepared and executed, the original can be sent to the Registry of Deeds for filing via an out of town law firm as long as the statement itself complies with the recording requirements of the York County Registry of Deeds and 10 M.R.S. § 3253, which provides as follows: 

 §3253. Dissolution unless claim filed 

1. Filing of claim. The lien under section 3252 is dissolved unless the claimant, within 90 days after ceasing to labor, furnish materials or perform services:  

A. Files in the office of the register of deeds in the county or registry district in which the building, wharf or
pier is situated a true statement of the amount due the claimant, with all just
credits given, together with a description of the property intended to be
covered by the lien sufficiently accurate to identify it and the names of the
owners, if known. The statement must be subscribed and sworn to by the person
claiming the lien, or by someone in the claimant's behalf, and recorded in a
book kept for that purpose by the register of deeds for the county or registry
district, who is entitled to the same fees as for recording mortgages; and 

B. Provides a copy of the statement under paragraph A to the owner or owners by ordinary mail. For purposes of this paragraph, a post office certificate of mailing the notice to the owner is
conclusive proof of receipt by the owner. 

2. Exemption for contract with owner. This section does not apply when the labor,
materials or services are furnished by a contract with the owner of the property affected.