How much is the web development cost for building an online marketplace like Airbnb or Clarity? And how much does regular maintenance cost? I have no web development experience, so will need to hire others for this.
Like every project, it "depends". Sorry, but that's the truth.
Here's how to make it cheaper:
1) Concentrate on one vertical, or thing you do well. This lets your shopping and checkout process be much more simplified. For Clarity, this is finding the right person to talk to, and putting two people on the phone together. If you try to do everything (calls, video, in-person meetings, local coffee connections, founder dating, etc) it'll be a nightmare to support all those workflows.
2) Try as hard as you can to stay away from being "local". Anything on the ground dramatically increases the pain in building out your marketplace. Clarity I love because there is no concept of cities, anyone can be anywhere. AirBNB has to onboard inventory in each city and have on the ground representation near where they have inventory.
3) Transparent, simple pricing. Clarity = Cost per minute * Number of Minutes. The second you try and get all fancy with your billables, people get confused and don't pay.
When selecting a technology, make sure you pick something where the cost to add features in (both time and $$$) is relatively simple. Additionally, avoid languages which require massive infrastructures (Java, .NET, etc).
I'd recommend Ruby/Rails or Python/Django. Both are incredibly fast at building out web projects. You may have success in Node but I've found it difficult when it comes to vanilla web applications.
If you stick to simplifying the project, the cost of maintenance will be minimal.