How large of a congregation are you planning to serve? Many parish nurses end up volunteering their time, not because they aren't valued, but because the churches cannot afford to pay them. My husband once served at a large metropolitan church with over 600 members (he was one of the two pastors, both full time) and had three volunteer parish nurses. The first parish nursing program I started was in a church with about 1000 members, small urban/suburban, and I was not paid. Currently my husband serves two rural churches and I'm doing some parish nursing but not to the extent that I did in my previous congregation.
In my previous church, there was very little room in the budget for many expenditures associated with parish nursing. The church paid for additional liability insurance because of the program and we received donations for equipment such as sphygmomanometers. We had an excellent parish nurse resource at our local hospital, fairly well-funded at the time, so all the churches in the area were able to get some materials that way.
You are blessed to be asked to develop a budget! Some churches, regardless of size, are unable (or unwilling, as with my previous church) to pay the pastor a living wage, so you are fortunate that your church is even willing to consider giving you a budget. They may or may not pay you. I think that's the biggest barrier to parish nursing---I would, quite frankly, do this full time but have yet to find a church that is willing to pay RN wages (or any wages, for that matter of fact...) Not saying this to discourage you, but you might want to get a ballpark figure from the pastor or the business manager or president of your congregation to see if they're thinking of paying you or not---and take your budget from there.
One thing for which I think you should ask in your budget is for the church to pay for at least part of the cost of your parish nurse preparation course. When I took it about eight years ago, the cost was around $500. My church did not pay for this but, luckily, I got a scholarship
from the hospital that took care of the cost. It was an amazing course, the standardized curriculum offered by the International Parish Nurse Resource Center, and well worth every penny, even if I would have had to pay out of pocket.
Also find out how many parish nurses your congregation wants/needs. In my first congregation, I was kept busy with my educational efforts and providing social support. I certainly could have used some help but most of the other nurses in the congregation were busy with paying jobs and their families, so I didn't have a lot of folks beating down the door to help with this ministry. In my current congregation, the needs are vastly different; we have some educational programs but not nearly at the same level that the previous church expected. The social supports are much closer here so I'm not doing that as much as I did in my previous church. I find that most of the time I help the pastor with health-related issues and visits to hospitalized parishioners and shut-ins. (As a pastor's wife, I also find that there's the expectation that the minister's spouse does a lot of volunteer work so I am very careful with my boundaries and don't spend as much time in this ministry as I probably could.)
If you haven't taken the basic preparation course, you will find it very useful in helping you determine an appropriate budget.
Blessings to you on this journey!