If you want to test customer interest in your idea via a landing page, and want to maximize learnings and minimize time spent building the landing page, there are a few options.
1. If you want to rapidly build out a website, the easiest thing is one of the wysiwig platforms. Examples: Squarespace, Wix, Weebly. Squarespace costs money, other two cost less money if you are ok with the URL showing their domain (URL forwarding will take a little more time and/or money). For email capture: All of the above have embedded forms. That said - you can also embed URL from Google Forms or Typeform. The latter is quite full featured and we use it for a lot of programs.
2. If you want to run real experiments (e.g. A/B testing, multivariate) and want to quantify funnel metrics and also run an email campaign out of the same platform, unbounce.com or quickmvp.com are good bets. Optimizely is a good platform for A/B testing as well.
For tips on running landing page experiments to test purchase interest, have a look at Elaine Chen's article on Xconomy.