Hello,
There are two approaches to build a website like Elance:
1. Use some existing elance/freelancer script, which normally cost $50 - $200 Normally this kind of scripts are very poorly built and you can use it if you want to get something up and running quick and not planning to scale a lot. All we can do is customize look and feel of these scripts, because they're pretty bugging and for a flat rate we can stuck fixing bugs for developers. Alternatively we can fix bugs and implement some features on a hourly basis (30 $ per hour), but it will be hard to customize them a lot and normally this kind of scripts are not well designed for growth.
2. Second approach is to build a website on a framework like CakePHP from scratch. Advantages of this approach is that you get a custom solution, tailored to your needs. Disadvantages are longer time frame and higher budget (at least 4 months and $10 000 usd for full cycle). This is the way to go if you want to compete with elance. Using a first approach you can simply waste money, but users won't use your website, because they have a better marketplaces available.
Let us know which way will fit your needs better.
We are sure we can find the best solution foe development according to your goals and time/budget frames.
Best regards,
A2 Design