Don't want to be too negative but the entire post could have been shortened to 'put it on Flippa'. Then, the other advice is quite obvious.

Flippa isn't bad but if your side project is good for anything and you want to achieve a better price, do a small M&A process: Identify potential buyers yourself, approach them and keep the approaches synced to create and keep up competition. Also you could combine this manual leadgen with Flippa.