hi, I think you already accept that raw feeding is the best diet, so lets move on to addressing your two main questions.
Feeding raw CAN be expensive, but many of us buy in bulk, or catch bargains at the local butchers. Butchers can really be your friend here, and I cannot emphasise enough how useful it is to go in and chat with as many butchers as you can locally. We can help you with a list of questions to ask butchers.
This will help you get an idea of what foods you can buy locally, and some butchers are happy to set aside not 100% great (for humans) cuts of meet.
You're unlikely to get everything at the local butcher, and that leads us onto ordering online. I would say that I order around 95% of our girls food online. I do get most of the organs locally as the quantities I need to buy online make it unfeasible. Maybe one of the members your side of the pond can suggest where to order from, but I know a few use online suppliers.
holisticferretforum.com/natural-diet/raw-and-whole-prey-providers/Commercial grinds undoubtedly take some of the work out of preparing a raw diet, but they do this at an increase in cost. Basically because someone else is doing the work. Grinds are a good starting point, as you can buy them with a set amount of bone (10-15%) for bone in meals, or bone free for muscle meals. You simply then weight out an amount (2 ounces) per meal.
Grinds are nothing more than just ground up feed, which needs no further cutting up.
One thing I would say about grinds is to try and keep to one protein in a grind and not use mixed or unbalanced grinds, this way, if your boys don't like it, or you discover they have an allergy to a certain protein, then it's much easier to eliminate it from their diet. If you feed a mixed grind, you can't tell what they don't like or react badly too. Allergic reactions to foods are RARE, but it's something to be ware of.
Proteins - You'll hear a lot about proteins, and it can be a little misleading. When we refer to a protein, it's simply a meat source. So feeding Chicken, Pork, and Turkey based meals in a week would be 3 proteins. It doesn't matter if these are bone in or muscle, the importance is the variety of proteins fed. You want a minimum of 3 in a week.
It's complicated? Planning, planning and, oh yeah, planning! Getting a good simple plan is key to making raw feeding NOT complicated. First is a menu plan, which we'll help you with, after you chat to butchers locally and see what's available online in your state. The basic frakenprey menu is a really good starting point:
holisticferretforum.com/natural-diet/raw-diet-the-meat-of-the-site/basic-frankenprey-menu/Transitioning onto raw - No two ferrets transition the same, some just do it without any effort, others take time. Your boys are going to be imprinted onto their food by now, so they'll need to learn that this new stuff is food. Without doubt the best way to transition is with the soup method, this involves blending up a raw meat puree to feed them. I have often thought that soup was a bad name as it implies that it's cooked. All a soup is is pureed raw meat mixed with some water, and bone meal to make a smooth paste. Once you get them eating that, you slowly add it slivers of meat, and build up to small chunks of meat.
You'll need a small kitchen blender to make soups, and I would suggest buying a separate one, as it will take on a certain aroma, however well you clean it.
holisticferretforum.com/natural-diet/raw-diet-the-meat-of-the-site/raw-soup-recipe/Anyway, I know that's a long reply. Ask further questions, follow the links I posted and above all else, you can't go wrong if you ask questions and plan. It's not hard, just a little daunting to start off, but plenty of us have done it and are here to help. I am sure others will be along with words of encouragement.
Cheers