Hi,
I graduated from Clonlara over a decade ago now. It was, at least from my perspective as a student, a nice balance between providing documentation (including grades, at least for high school) and giving considerable leeway for us to make our own plan of study. For some things we were very formal (we used a real curriculum for math), while for others we were more experiential (e.g., for American or Michigan history we did a lot of traveling and going to museums and such, which they let us count as study hours). Grades were the grades my parents gave me, and were recorded on an official transcript which was mailed to colleges when I applied, along with a course list and descriptions, which we were also responsible for generating. I don't really remember what was done for the lower grades -- here it's only high school transcripts that you need for college applications. There were other requirements for graduation, including a very long essay test covering a variety of subjects, taken at home, and a service requirement.
With regard to paying for a separate curriculum, you don't really need to do that unless you want to, and even then you can do it in many cases per subject. For example, for most of the liberal arts courses you don't need a textbook even, you can go to the library and get age-appropriate (or level-appropriate) books for your child to read. For science and math, you'll probably want textbooks, but you don't need current editions and can get a lot of them on ebay or used on Amazon or equivalent. Even then, just buying a textbook is usually a lot cheaper than buying a curriculum (they include such things as lesson plans, etc.). The Clonlara teachers can help you figure out where your child should be academically, although you will of course be hearing more of an American/Michigainian standpoint on this, where we are far less rigorous than many countries. Since there is nearly complete freedom from Clonlara's perspective (other than their high school graduation requirements), you could also see what the local school is doing for their curriculum and copy it.
As far as international students, I dunno -- you'd have to ask them. They might be a little slower answering this time of year. You could call them, although I realize that's a bit hard internationally. They were very responsive when I was a student.
Best,
Anka