want an expert on wordpress to fix error:Could not an create order a slow website others problems

Hi, a wordpress website that was recently build is having some problems. The site will say page not available before loading, the site is slow on some pages, the shopping cart is not showing on the phone and on the tablet on the vertical position, it shows when horizontal when placing an order it will say: unable to create an order. also there is an issue with the currency usd and canadian dollars are showing the same amount. it was working before. site should be set up to usd and able to convert to canadian dollar An expert can fix these things fast. My budget is $ 15 dollars. If you can help out for the 15 dollars please do. If you can not please do not apply thank you