Patent infringement is a highly charged subject, and I have seen how it affects the patent owner. A lawsuit would seem like a wonderful solution. But, what should it cost?
Though I have heard many numbers, it is all just hearsay. Even so, it may be helpful to say it.
A contingency attorney might take the case, but may require an ownership interest in your company of 50 percent or higher. Is it worth it? Maybe so, if that's the only way to go forward. And why the high ownership interest? Easy – to have control to ensure payment in event of a victory.
A very small law firm or individual attorney will often charge less than a large firm. I have heard stories wherein a plaintiff might pay somewhere between 20k and 60k, depending on if/when it settles. Higher numbers are possible when it goes to trial and there are many issues. Is this a good value? That depends – if you can only afford that much, then there's simply no choice.
A big company practically must use a large law firm for its reputation and size. There is great variation, but one should expect to pay for that large size and reputation. I have heard a number of experienced litigators say to simply add a zero to the numbers used for a small law firm. Is it worth it? That depends, but I have seen examples where it was well worth having a large firm do the litigation.
Where's that money go, anyway? Well, a portion goes to filing or answering the Complaint; attending to discovery and motions related to discovery; depositions and court reporter costs; various court hearings where attendance is required; and finally for the trial itself (if it goes that far).
If you're the plaintiff, you'll have some control over the costs. If you raise more issues, then the cost will be higher. Or, if you challenge everything using Motions, then your costs will skyrocket.
If you're the defendant, and the issues are simple, and you are confident of winning, costs tend to be much less. If you're the defendant, the issues are complex, and you fear you might lose, then costs tend to skyrocket. I have heard anecdotal reports of costs in the millions in such cases.
Every case is different, and the above is not legal advice. To get legal advice, you'd need to consult a patent litigation attorney and discuss the details of the case.