You've put a lot of time into this, so it's worth sticking in there and taking the advice people are giving you. The current approach is clearly not working, and this forum is basically the bulk of your potential customers.
Coz is giving very good advice. People will buy the software if they see the value in it - the number of hours you put in yourself is irrelevant unfortunately. I put in similar hours to some of my larger books, and they only sell for €30 each
As you have appeared out of nowhere, with no web site and no independent reviews, you will definitely benefit from providing review copies to a couple of MPC60 power users here, such as Clint - if they say it's good, then people here will buy it. You also need to get more beta testers on board, having a single tester is not ideal. It is also highly unlikely that there will be no bugs, no matter how much work was put into it.
However the problem is that if/when the bugs do appear, people need assurance that the bugs will be fixed. Currently you are not assuring that, so it will make people weary of paying.
I think if you are not willing to provide support nor continued bug fixing or further development, you should definitely consider the opportunity of selling your code to that third party for €x000. I may also be able to put the word out to some other developers who may be interested in taking it on, or perhaps working in partnership with you.
EDIT - as someone mentioned to me via PM, you should also contact Roger Linn to ensure there's no copyright issues involved - I'm sure anyone buying the code from you will ultimately want that assurance as well.