Ask HN: Best way to build Yelp for X?

Dear HN:

What's the best or fastest way to build a Yelp for X site?

This is for a geographically-oriented niche market where users would submit reviews of a particular type of service provider. It wouldn't be pure Yelp because this industry has some unique characteristics. But it would be pretty close.

We'd also need a discussion forum, also geographically-oriented. We might be able to create it using Discourse depending on how easily Discourse can be customized.

Is there a SaaS that can make this possible? Toolkits?

I could develop it from scratch myself, but it would take months and probably wouldn't be as good as what a third party would provide. Ideas?