I am a very experienced web designer/developer who has been working in the industry since 1994. I have worked on projects from small websites up to 6-figure development projects. I have been freelance for the entirety of my career and so I am very well versed in time management and meeting aggressive deadlines. I am a native English speaker.
You're not going to be able to get your website to be responsive without updated your shopping cart at the same time. It's just not possible, as the shopping cart is what generates the page content.
I would recommend rebuilding your website in WordPress, to allow you to easily make changes and updates in the future. This will also allow your website to be easily viewable on mobile devices such as smartphones and tablets. I would also recommend you use WooCommerce for your shopping cart, as it is the industry leader in e-commerce solutions for WordPress. My quote will also includes basic SEO work to help your website get found.
Obviously this is not all going to happen for $150, so if you're interested in doing the entire project (website and shopping cart) I will provide you with a proper bid.
I am currently trying to get myself established on Freelancer, so I will give you a heavily discounted price. You'll be getting great value for your money! I would love for you to be my first project on this site.
All the best,
Brandon Snow