CGB Perkins,
I am an immigration attorney. However, it is not my intention to get your business as it is contrary to the forum regulations. However, I would like to answer your question from a professional perspective.
First of all, please note that there are several categories available for residing in Costa Rica legally. Some of them will allow you to become a permanent resident and subsequently a citizen, some other categories will not allow you to follow that path.
The application process is not necessarily difficult, but it not easy either. If you are a careful reader and have a little bit of patience, you will be able to prepare your application yourself. This is the website for the Immigration Department if you would like to check it. Here, you will find all of the information you will need.
If it is too complicated for you or you are too busy, it is then recommended for you to hire an attorney. Make sure that it is an attorney. Only attorneys are allowed to assist individuals with the application process. So, you either do it yourself or hire an attorney. There are agencies and people out there that provide immigration services and are not registered attorneys. This is an issue, because if something goes wrong, you will have no recourse against them. If you hire an attorney and he or she is negligent, you can then file a complaint with the Bar Association.
As far as the costs are concerned, the attorney's fees cannot be less than $1000 USD. This is indicated in the law. No attorney can charge less than that. Otherwise, they will be breaking the law. You can expect an attorney to charge somewhere between $1000 and $2000 for preparing and filing the application. Regarding the expenses, it will cost you an additional $1000 USD in related costs for the application, depending on the country that you are from, as you will be required to pay a security deposit once the application is approved. On average a temporary residence application for a US citizen will cost $3000 USD (approx).
The processing time can take up to 18 months from the moment you start obtaining the required documents until the moment that you obtain your DIMEX. Whether it is a nightmare, it will depend on whether you do it yourself, or whether you hire an attorney and how good that attorney will be. Remember, in the legal business as in any business, you get what you pay for.
I hope this information is useful.