This statement is confusing. Do you mean that you want a free tool to do a commercial project or a free tool (shareware) that you can evaluate so that you can then purchase it and evaluate it for commercial projects ?
What's the confusion? If the license says that a tool can't be used in a commercial setting, then it can't be used in a commercial setting, it's as simple as that.
I'd advise to look for a non-free tool, though. If the company/project is large enough that using an ER tool can make people more productive, then it has enough of a budget to pay for. Such apps are not that expensive, and not all that many people would need to use it. You'd also most likely be saving yourself and the other users a lot of time spent figuring out the free tool (which would typically not have good documentation).