I like this guy from Forge World, but there are certainly ways to make your own Space Marine Company Champion without going out and buying this model. The pose is pretty cool and I love the stylized armour, but I look at this and start thinking about what I can do with the stuff I have to make my own Champion model.
There aren't many things on this guy we couldn't reproduce without too much trouble. The simple eagle backpack is a nice touch. The helmet crest is another popular item these days to set character models apart. You can make your own (I have), but I'd suggest buying them third party as it's not worth the pain to try and make them from scratch.
I know Secret Weapon minis has them in different shapes and sizes. I mentioned it the other week when I posted about some of the things you can do to make your own Command squad upgrades.
Adding smaller elements like Terminator honors and skulls is always a winner. You can never go wrong with the occasional skull thrown in there. Nothing says you're dangerous more than a skull hanging from your belt. As you can tell from the guy above, he means all business having two of them hanging from his.
It doesn't have to be much
You don't have to make huge changes to a model to make him stand out from the rest of the army. It might be as simple as different painted shoulderpads or a slightly converted helmet that no other model is sporting.
Another easy option is a weapon swap. I recently did it with the Dark Vengeance Librarian I'm currently working on. Nothing else was done to him other than to swap out his weapon for a different one. Completely new feel to the model now.
Don't forget the base
Maybe one of the easiest ways to make a model stand out is to look at what you mount him on. Changing his base and elevating him on a small rock outcropping or toppled wall can change the look of a model in an instant.
The FW guys did it with their model. He's not standing on the basic flat base there, he's on top of some debris he no doubtedly caused with his coolness.
Did I do it wrong?
A while ago, I set out to write a article on HQ models (Champions would fit in here too) and it turned into a three part series talking about modeling and painting your HQ model and what you can accomplish by adding or leaving out certain aspects.
For those looking for a little more on the whole idea behind the "why" we should or shouldn't model certain things, it might be worth the read. You can find the series here. Each one links to the next article and it's a quick read. There's even some tactical advice in there as well and I don't write anything on tactics.
Setting your Champion apart from the rest of your force doesn't have to be hard or expensive to do. Sure you can buy the model, but it's just as easy to look at what you have, think about how you want him to stand out and be creative. You'll probably save yourself some money in the long run too.
Make sure to check out these posts as they might help:
How to make your own Command squad upgrades
Did I build and paint my HQ wrong?