How much time does it take to make a website like this : http://www.rosegal.com & how much money it costs.

The site you linked in your post actually looks like a shopping cart template that was adapted. Imo there are some issues with the site from a development (e.g.: non-responsive to browser sizes) and a design (e.g.: the sizing and color choices for the slider and banner up top).

When you are asking about making the site you have to look at it from at least 2 sides. One is the code for the site. I am pretty sure that a good developer can rip up the code for that in 2 or 3 days. Then there is filling the site with content. And that much more of a hassle if you are doing it all yourself (implementing every product, writing every product description, taking every picture and editing it, etc). Often enough people don't do that though and instead use the wholeseller's stock photos and stock item descriptions which is bad for the SEO.

As for how much does it cost. Anywhere from 10k to $250.

Expensive End: Let's say your developer charges about $100 / hour. He is busy for about 25 hours on the site. Since your don't stock the items and are drop shipping instead, you don't take new pics. But you have a designer run each one of them through photoshop. Lets say you start with 3k pictures and each one takes 2 minutes to edit - that is 100 hours right there. At about $50 per hour that makes around 5k. Then you have a data entry specialist that types all the descriptions into your site and gets the stuff into the structure. They work for about $10 - 15 per hour but it will be easy for them to burn through the remaining 2.5k.

Cheap end: Go with a template from a shopping platform like bigcommerce, vollusion, woocommerce or shopify. Pay monthly about $25-50 for the use of the template. Don't change the pictures and use stock. Hire data entry guy from India or Philippines on Fiverr or Freelance and get the whole implementation done for $150-400. Yes, there will be spelling and formatting mistakes but you get it done cheap.

If you have your niche and suppliers, go with one of the big ecommerce sites. They usually offer first month free membership and you can test your approach and traffic generation and see where you are at. After that you can take it to your own site.

Just my suggestion.

I agree with Falk, I might look at using Shopify or Magneto to help get your site going if you already have your product line set up.