first of all, here you can find a list of Steuerberater in Werl (7 in total):
You can click on the links to their websites to get a first impression of their work.
Concerning the price of a Steuerberater: in Germany there is a so called "Steuerberatergebührenverordnung". It regulates how much money a Steuerberater can demand for certain tasks. But these are just guidelines: he can ask for more or less money depending on the complexity of the task. So the price you have to pay for his/her services can be negotiable.
Therefore you will have to get in contact with the chancelleries listed above in person.
There are calculation tools online that can help you to estimate the costs in advance (their estimations are based on the "Steuerberatergebührenverordnung"). I would suggest that you try out one of them to get a feeling for what it might cost and to be able to estimate if the offer that a Steuerberater is giving you is fair-priced or not.
You can use this website for example:
On the site linked above you can choose a package of typical tasks a Steuerberater is doing for you or you can pick your personal mix of tasks from the list. Then you can adapt the values to get an estimated sum of costs.
I know that the website is in German (but if I remember correctly your German is pretty well). Nonetheless this topic is quite complicated and confusing. So if there are further questions feel free to ask - the community and I will try our best to help you out with this.
I hope my answer was helpful for you