You seem to have the idea right whereby posting on communities like this will attract those who, like myself, offer consultancy services and can co-create a business plan for you. In today's wired community, it doesn't really matter where the consultant is based as information can be easily gathered to help in developing a business plan.
The cost of creating the business plan would vary based on how you intend to use it as it can vary in length and detail from 20 pages, used for your own benefit as a roadmap, to a 200+ page document, if its intended use is to raise funds through investors or financial institutions.
In any case, I would advise that you begin by having the consultant generate a feasibility study for your venture as it provides you with top line findings on many variables letting you know whether you should invest further in developing the business plan as they could get pricey. While it would appear that a conducting a feasibility study comes as an added expense, the information it provides would come in use for the business plan and as such driving down the cost of developing one later should your venture prove feasible. Additionally, a feasibility study is much faster to create and would also allow you to get a feel of how well you worked with that consultant before diving in to a bigger challenge and investment into developing your plans and can negotiate a special price if they're to continue working on it.
I hope this helped and do not hesitate to reach out if I could be of assistance.
You should probably use a few of the templates available online to get a first draft of your business plan. Once complete, you can speak to a professional, maybe on zintro, fiverr or freelancer to convert the raw data/bullet points into a polished plan which you can use. You doing the first draft will ensure that you think through your business and you may discover things that you have not thought through before. I sometimes write business plans for some of my ideas and mid-way, I come across expenses I hadn't thought about earlier or additional sources of income or even marketing ideas for the business.
Writing a business plan is always exciting and let me know how it goes!