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OK. Maybe free is a stretch. In fact, if you've got a modern marketing system, landing pages should have a marginal cost of zero. Why? Because your site shouldn't be a pretty brochure - it should be a lead generation machine. 
The only way that is possible is if you have a variety of compelling and targeted calls-to-action on your site and collect leads via landing pages. Here at HubSpot we actually have more than 500 - we are a bit prolific, but many customers have upwards of 30 offers and landing pages!
Too many companies today still rely on third party web developers or IT departments to build custom landing pages every time marketing needs to launch a new campaign. That can mean anything from $500 per landing page to an internal charge back and a two week wait to get to the top of IT's priority list. Why be held hostage when you need to drive leads NOW?
The three reasons you need a system to publish landing pages at a marginal cost of zero:
1) Marketing today is agile.
You need to be able to respond to a market shift or news event on a dime. What if a new regulation was passed in your industry and your executives had a strong vision of what this means for your customers? Can you afford to wait two weeks to launch your campaign? No. You need to be able to build a campaign on the fly - email is fast, people register 2-3 days out nowadays and you can create the content fast. Be the first to the punch with ready offers that you control!
2) Marketing today must be targeted.
Too many small businesses have only 'contact us' offers on their website. Most buyers aren't going to contact you unless they've alreayd 'sold themselves'. What about those who are interested, but need help to uncover potential solutions - you really want to be there early to help shape the buying process for those leads. The only way to do that is by having targeted landing pages for different offers, be it an ebook, webinar or free sample. Each type of buyer at each stage of the buying cycle is looking for something different and in most cases is is NOT to contact you. Dont' let a long delay or, worse, a $500 price tag per landing page hold you up from generating leads online.
3) Marketing assets, especially landing pages, should be constantly tested & measured.
How do you know if one campaign or landing page is working better than another? You have to build them and compare them - also known as A/B testing. If it costs you an arm and a leg or is a big hassle, that's probably going to diminish the amount of testing you will do. Even small companies can and should be testing their CTAs and landing pages because every bit of conversion optimization means more leads and potential customers to grow your business. The shot below shows how two of HubSpot's similar, but different, landing pages perform indicating a higher conversion rate for our Kit. More Kits please!
Those three reasons all add up to helping you grow your business. The good news is that there are a lot of tools available to SMBs today to make the creation of landing pages easy and, after a small initial investment, virtually free!
Whether you choose to use HubSpot's inbound marketing software for its many features, including unlimited easy-to-build landing pages, a dedicated landing page tool like Performable's or even learn to code them yourself, the marginal cost to you should be close to zero. Once you have made the investment to build one landing page, you are in a position to build them quickly and easily going forward.
How do you create and test landing pages today?
On-Demand Webinar: Optimizing 60 Landing Pages in 60 Minutes