Rachel has it 100% right. I’ve seen websites where people have just asked for a website and paid GBP 500 and they got a website but not really what they wanted. The more time you spend specifying what you want the more likely you are to get something that you want. There are some other things that you might want to specify that you may not have though of:
1. Do you want it to only work on a PC, a tablet, a phone?
2. Do you want to be able to update content yourself or will you always ask the developers
3. How fast do you want the site to be? Which visitors are those for? If it is only local people you may not want the site hosted in the US
4. How many people do you want updating the site? Just yourself, colleagues as well?
5. Who is going to maintain the site? Most ‘systems’ require security updates to avoid being hacked into. Remember that people don’t hack in to see your secrets – they hack in to compromise your visitors computers. You need this in the service contract
6. What is the rework cost? It is not unusual to have a low upfront cost and then rip you on rework. Discuss it up front.
500 is way to cheap and it may not be as much as 5000 but it will be getting up there.
Also, and very importantly, having a good site doesn’t mean you will rank well but it will help. If spending money on a good site got you first page google then everyone would do it. Getting seen will also be up to you getting links in from people who you have done work for, getting reviews (maybe you need a reviews section but that is risky), photos are always good. You need to ask your supplier what you need to be doing to get your ranking up