The recourse to not paying off is foreclosure, or a rewrite/modification of the note. 

You don't ALWAYS need to be polite - - Your lease should have forbidden all modifications by the tenant. 

Personally I'd try and work the price down, even if it's just to cover the costs of the modifications.

I have a 900sq ft 3bd ranch and a 1.5 ton ac unit plus new furnace and some duct work modifications was 5500 for me.

Depending on your lease and state laws, a modification of this that I would recommend is to simply decline partial payments all together.  

Over 3 years, we had completed 2 loans and 7 modifications.

I know it may seem complicated but it is really same idea when you transfer the deed to the property.Regarding modification during the sale of the note - if not disclosed than I will find it unacceptable and will go along the lines of misrepresentation by the note seller. 

CHANGE THIS TO NO MODIFICATIONS ALLOWED BY TENANT.

So what those attorney fees are for are to draft up the loan modification paperwork which will reference the original deed of trust and will get recorded.  

CapitalRepairImprovements that "put" property in a better operating conditionImprovements that "keep" property in efficient operating conditionRestores the property to a "like new" conditionRestores the property to its previous conditionAddition of new or replacement components or material sub-components to propertyProtects the underlying property through routine maintenanceAddition of upgrades or modifications to propertyIncidental Repair to propertyEnhances the value of the property in the nature of a bettermentExtends the useful life of the propertyImproves the efficiency of the propertyImproves the quality of the propertyIncreases the strength of the propertyIncreases the capacity of the propertyAmeliorates a material condition or defecAdapts the property to a new usePlan of Rehabilitation Doctrine