Many of our members who like their current website, simply install a new instance of Wordpress (with Market Theme), into a subfolder named "store" or something.

Then, on their main website navigation, they simply put in a new link to this subfolder.

Then, you can modify the coloring and logo of your Market Theme store to match your main website.

You don't need to purchase anything additional.

All you need to do is create a new folder off of your main root folder that your current website is in.  You can name it "store" or something.  You can create it either manually via FTP program like FileZilla — or through your "File Manager" tool in your web hosting control panel.

To install a new instance of Wordpress into that new folder, you can do it one of possibly two ways.

1.  You can FTP up the Wordpress files, into the newly created "store" folder, and do a manual installation of Wordpress according to the setup instructions in the Wordpress package.

2.  It's also possible that your web host has an easy "one-click" type Wordpress installer script.  Many hosts have this, and it's really nice.  You would see it in your control panel area of your hosting account area.  If you have "cPanel" as your hosting control panel, then you might have a script in there named "Fantastico".  If you do, then use that because it's really easy.  You'd just choose that option, then the Install Wordpress option, and then enter "store" as the subfolder to install into.

I can't tell you with too much detail, because I'm not sure the host you are using — but a lot of hosts use "cPanel", which generally includes the "Fantastico" script.

I hope this helps.