In reference to @Peter Walther post about foreclosure, the following is copy & pasted directly from the State Bar of Wisconsin Form 11-2003 Land Contract:"Purchaser agrees that in the event of a default in the payment of principal or interest which continues for a period ofdays following the due date or a default in performance of any other obligation of Purchaser which continuesfor a period of days following written notice thereof by Vendor (delivered personally or mailed by certifiedmail), the entire outstanding balance under this contract shall become immediately due and payable at Vendor's optionand without notice (which Purchaser hereby waives), and Vendor may singly, alternatively or in combination: (i)terminate this Contract and either recover the Property through strict foreclosure or have the Property sold by foreclosuresale; in either event, with a period of redemption, in the court's discretion, to be conditioned on full payment of the entireoutstanding balance, with interest thereon from the date of default and other amounts due hereunder (failing which allamounts previously paid by Purchaser shall be forfeited as liquidated damages for failure to fulfill this Contract and asrental for the Property); (ii) sue for specific performance of this Contract; (iii) sue for the unpaid purchase price or anyportion thereof; (iv) declare this Contract at an end and remove this Contract as a cloud on title in a quiet-title action if theequitable interest of Purchaser is insignificant; (v) have Purchaser ejected from possession of the Property and have areceiver appointed to collect any rents, issues or profits; or (vi) pursue any other remedy available in law or equity.

If it's vacant, nobody makes contact and locks get changed.Now, if they dig in and require you filing to eject them, that has to wait until you get the deed.

Then it's not just an eviction to resolve, it's an ejectment (foreclosure).

If you did not pay for a policy, I recommend you hire a good real estate attorney, the solution may be a simple as an ejectment action or, depending on the specific facts, the solution may be more complex. 

What should be the minimum purchase cost of a Tax Certificates be considering ROI of filing Ejection Notice and other legal things.

However, if a tenant holds over, after being asked to leave the premises for a lawfully valid reason, and it goes to court, the cost to the landlord can become substantially more.Depending on the laws of the jurisdiction, when the eviction process ends up in court, it may also be known as unlawful detainer, summary possession, summary dispossess, summary process, forcible detainer, ejectment, and repossession, among other terms.

I have a tax deed for a Jefferson County property and am considering ejectment. 

-take steps to immediately eject your neighbor.   

Legal aid said I need to file another summary ejectment.

provided, however, that private property owners or persons in legal control of private property through a lease, rental agreement, licensing agreement, contract, or any other agreement to control access to such private property shall have the right to exclude or eject a person who is in possession of a weapon or long gun on their private property.."