@Bjorn Ahlblad skipped you on the reply, but I'm estimating $1000 - $1100 per month based on similar sized homes in the area.  

I think understanding what exactly you're planning to do, will help you get a better estimate of the cost.

Another option could be to rent it out (estimated rent 3,000-3,200 per month)

They provided us with an estimate for septic system repairs done by a reputable company; however, when we had our usual company come out to do the repairs they found that the soil was not suitable and they would have to reach out to the county to run (perc) tests and to give the "okay" to continue work.

This way they (end buyer/investor) have the flexibility to negotiate the deal based on the wholesaler's fee instead of the lack of flexibility that seems to often come with the wholesalers inability to correctly estimate rehab costs and run accurate comps.  

The estimate selling market for the house is about 410k.

I'm for now just going off the conservative estimate of a very BROAD ballpark from a friend who works in insurance.  

The reason my loan delayed (generally it takes 7 days in our case it took 18 days) is due to Covid-19/refinance issues for lender and the reason my loan denied is due to change in lending terms for Jumbo Loan they requested 20% down and 15 months of reserve (Lender Estimate is for 15% down and 6 months reserve).

The evaluation tools on this site were instrumental in keeping in line with the estimated cost.  

And the 850-950 euro estimation is based on also long-term renting but in a bigger market?