Darren:
You ask a very legitimate question.
If you REALLY want to know how to get the best value for your money, you will need to hire multiple different freelancers, assign them to do the same or similar tasks, and compare the value you receive from them.
You might get the best value from a developer with a very high rate. She charged $75/hour, but she finished Task X in only 2 hours.
You might get the best value from a developer with a lower rate. He doesn't have a lot of experience, and he only charges $15/hour, but in 4 hours, he completed Task X.
You are likely to find some freelancers whose work and communication style you prefer over others. Some freelancers may deliver work too slowly for your needs. Some may deliver work but when you test it out, it is buggy or slow.
I would advise you to be open-minded about the technologies used to develop your project.
Maybe one developer provides you with a PHP-based solution that you really like, while another provides you with a solution using "Programming Language X," which you think looks cool, but the performance is really slow... It would not hurt to try different technologies, along with trying out different developers.
You don't need to get too deep into any one choice right at the beginningg. You can allow developers to work only an hour or two before evaluating their work. Or you can hire people to simply consult with you and talk to you (phone, Skype, email, chat) about their approach to your particular problem. What if you paid 8 different developers for 20 minutes of their time to discuss your project and their approach to it? You might spend only around $200, or maybe less, and end up being able to make a more informed decision.
It's not like exchanging dollars for yen, where there's a specific price listed for the day.
The one thing none of us here can do is tell you:
"For a custom ice cream ordering website, the right technology is PHP/LAMP stack, for which a developer should be paid between $30 and $35 an hour, and the project should take 30 hours to complete."
There's no way for us to do that. I suggest you plan to work with multiple people. You and your project manager should constantly evaluate their work and continue working with only those freelancers who provide you with the best value for your project.
