Marketing automation software is typically priced one of two ways: by the number of contacts in your database or by the number of emails you send each month. For example, the Growth Pardot plan costs $1,250 per month for email marketing, prospect tracking, lead nurturing and scoring, reporting, forms and landing pages, and standard Salesforce customer relationship management (CRM). This plan can be upgraded to two higher tiers, each of which offers additional features, plug-ins, and add-ons. However, all three Pardot plans give you capacity for 10,000 contacts.
Sales funnels are right for businesses that rely on a high degree of prospect interaction and engagement to make sales or close deals. Their sales process may be long and complex or they may be selling a high-ticket item that requires a lot of consideration by the customer. Both business-to-business (B2B) and business-to-consumer (B2C) businesses use sales funnels.

Let’s say you have a promotions page where you’re promoting a product via affiliate links. If you currently get 5,000 visits/month at a 2% conversion rate, you have 100 referrals. To get to 200 referrals, you can either focus on getting 5,000 more visitors, or simply increasing the conversion rate to 4%. Which sounds easier? Instead of spending months building domain authority with blogging and guest posts to get more organic traffic, you just have to increase the conversion rate by 2%. This can include landing page optimization, testing your calls-to-action, and having a conversion rate optimization strategy in place. By testing and optimizing your site, you’ll get far better results with much less effort.

Or, in some businesses, there’s only one thing to purchase–you just have to do so often. For example, let’s say you own a dairy farm and sell milk at the farmer’s market every week. Your regular customers buy the same two gallons of milk every week. You can’t move them farther down a sales funnel to buy something more, because that’s all you have–milk.
As a software engineer myself, I can tell you that building funnels from an application standpoint takes massive amounts of work. There's a great deal of coding and integration that's required here. From email systems to landing page implementations to credit card processing APIs, and everything in between, so many platforms need to "talk," that it takes the bar too high for the average marketer. 

^ Shashank SHEKHAR (2009-06-29). "Online Marketing System: Affiliate marketing". Feed Archived from the original on 2011-05-15. Retrieved 2011-04-20. During November 1994, CDNOW released its BuyWeb program. With this program CDNOW was the first non-adult website to launch the concept of an affiliate or associate program with its idea of click-through purchasing.