Don't use a common weatherstrip. You need a fridge gasket. They're made of a far more durable material than weatherstripping. It not only seals better but can be scrubbed when it's dirty.
As you found out, the OEM ones for Dometic fridges are ridiculously expensive. They charge what they do because they can. There are some alternatives however. Check out BA Refrigeration. They specialize in replacement parts and gaskets for residential and commercial fridges, but they will also make them for RV type fridges. They make them custom to fit, with welded seam corners.
They are much more reasonably priced than Dometic. You can also order a sample ring, and then just choose the profile that's closest to what you have. The most critical thing to get right is the thickness. If it's a hair too wide, that's OK. Just don't get one that's too thick or the door won't close properly.
Here's a link to their site and sample ring ordering page.
https://www.barefrigeration.com/refr...e-gasket-ring/