QuoteFX seems to be a good tool to handle sourcing events on-line, it's easy and quick to use.
You need to evaluate if it is really what you need though.
It depends on what you negotiate, and how often.
If you negotiate very different categories of material and services on a regular basis, it may be interesting for you to go for a more advanced solution, that will be configured according to your business model and specific requirements.
The monthly fee of QuoteFX seems a little bit high, but it's not if there is no long term commitment required.
My advice would be : unless you already know you need a more advanced model, go for QuoteFX for a couple of events. It will help you explore eSourcing capabilities, and find out more easily what your real needs are.
Do not hesitate to contact me if you want more info on what to look for.