It could vary from ERP to ERP. However remember that all ERPs are not the same and as such a cost comparison between ERPs would not be a useful activity.
A lower cost ERP would not necessarily mean an in-adequate ERP. At the same time a high priced ERP would not mean that it is the best and most suitable to your needs.
A good, well implemented ERP, with a good provider, who can support you in Change management and help you control more and more things over a period of time is in-valuable.
It will cover your ROI in a very short time.
It will cut down your cost of hiring expensive Managers, at the same time ensuring improvement in the Quality & Quantity of work done.
It will also cut on your expenses and increase your profits.