Hi , I am a startup founder based in Singapore. I am a consultant to multiple startups in Singapore. Answering your questions below -
1) I have been using Nodejs from around 5 years and I would rate myself 9/10. I am quite good with AngularJS, MongoDB , Redis, Amazon AWS etc. I have used Ruby on Rails, Python in the past but Nodejs is my favorite now.
2) I can start immediately. I can spend around 15-20 hours every week on this project.
3) If I were to build a price comparison site, I would use NodeJS , MongoDB, AngularJS as the technical stack. The reasons are below -
Nodejs - Nodejs is asynchronous in nature and hence obviously the best choice to build crawlers, web-scrapers etc. Nodejs already has a lot of web-scraping libraries. Also NodeJS's event-driven nature makes it the best choice for building something which has a lot of parallel activities all the time.
Mongodb - MongoDB is noSQL and good as its scalable and can fit in any kind of custom data. When we build a price-comparison site, there might be non-standard data and Mongo can adapt to it.
AngularJS would make building the dashboard very easy as it would be so easy to pull in data and so realtime prices etc.
I havent exactly built a price-comparison site but built lot of other ecommerce stuff - hotel management system, appointment booking system, realtime surveys, booking aggregator , distributed games, etc