There is no simple answer to this question. The cost depends on many things, eg. the complexity of the project, graphics, etc. A rough cost can be calculated after some general requirements are set. I do not act with a surprise - I try to determine in as much detail as possible the customer's needs and the cost before I start the main work.
You should begin with determining your needs as precisely as possible. You should more or less know what the purpose of your website will be, whether it should target local or national (worldwide?) customers, whether it should contain only most important information or a more detailed presentation (internet shop?) etc. Then you should think about how much money and time you can assign to this. Having this information you can contact me in order to determine the next steps. Obviously I can help in every step of the way, including the choice of hosting service, domain registration, search engine optimization etc.
For your website to be visible on the web you need a server. You should therefore buy a space on such a server (a hosting account). The cost may vary considerably, depending on the hosting provider - it can range from 100 EUR to 1000 EUR per year. Obviously the choice is not only about the price, but also about the quality of service. The cheapest accounts do not give you guarantee that the quality of their service will be high, neither do the expensive ones. You must rely on the provider's reputation.
Most often you also need to register a domain (an Internet address, eg. www.yourcompany.com). The first year is usually for a very low price or even free, then you pay yearly (usually 10-20 EUR).
Finally you must add the cost of the deisgn and implementation of the website on the server (see above). I can help you in every above-mentioned aspect.
Search engines do not "like" pages with errors. When they are corrected, it can result in a higher position of your website in search results. This means that a prospective customer will have a better chance of finding your company.
Code errors can also cause problems in rendering your pages in various web browsers on various computers. Even if they work perfectly on your machine, those code errors can cause your website to display in a different way on another machine.
Finally, those errors can cause your pages to load longer, which is always undesirable and can discourage users.
The position of a website in search results (eg. in Google) depends on many factors. Some of them are directly related to the quality of the website itself (proper code, standards compliance, keyword arrangement etc.). However, sometimes it is not enough and SEO (Search Engine Optimization) services are needed. It is worth looking for companies that calculate their price directly on a position your website reaches in search results. This way you pay for the result, which is fair. You should be careful when you see offers "guaranteeing" your website to reach no. 1 spot. No one can give such a guarantee.
After the website is created all the copyright belongs to the customer, who is free to use all the elements (graphics, code, etc.) in whatever way they wish, unless particular elements are subject to a specific licence.
Yes, provided you do not break the copyright. If the photos you want to publish have been found on the Internet without a licence clearly indicating the possibility to use them for free, you will break the law. On the other hand, if they are photos of your premises, made by you, you may publish them.