I am in the initial stages of the talks. The manager has mentioned about money being involved, I was looking for a "%age of future royalties of the sale" kinda thing. Yes the product can be of more than $20K as per me.
A simple cash deal is probably something you can do yourself, or with very little assistance. Anything more complicated requires an experienced attorney.
Don't forget that by providing you with sales / revenue / customer management they are bringing a lot of value to the table.
Who will develop the product ongoingly? Who will provide patches and support? These might seem like obvious questions to you but they must be discussed and written in a contract.
Finally, make sure your contract includes sufficient legal protection. i.e. the product has no guarantees and you are not liable for any cost, damages or loss, direct or indirect. If things go ahead then you definitely need a lawyer to help you with this.