You must find at least one distribution channel, that will work for you. It is, the cost of user acquisition will be lower than the lifetime value of the customer. If you find it, you have a good business. Otherwise, you’re finished.
Depending on what your product is and to whom you’re selling it, there are different approaches to sales. Most likely, you need only one of them.
When the average size of the deal is $1M - $100M, the CEO is the salesperson. People will not want to talk to the VP of Sales.
This is when the average size of the deal is $10.000 - $100.000. To sell such valuable products, you need a good seller that will contact potential customers directly.
Marketing and advertising.
When the product price is around $100, and you have relatively easy access to potential customers, then the regular advertising channels should be good enough for you.
When the advertisement channels are too expensive to use (because of the low price of your product), then the viral marketing might be the best option. It’s cheap and it’s fast.