You are not the first and not the last to be frustrated by the Algeria/Morocco border, but no one has figured out an obvious way around it yet. Your route through Mauritania is fine, but northern Mali is considered difficult at best, and the other option through Niger is only slightly better at the moment. Maybe you already know this....but if not, I suggest that you've got some research to do before getting to North Africa. Lots of information about all of this in Hubb forums.

My tickets (with bike) to and from Morocco cost about 30 euros each way. You can go to Morocco, back to Spain, then ferry to Algeria and will have only spent an extra 60 euros on ferries if you can find similar fares. Then you can continue across Algeria, Tunisia, Libya and Egypt. But if you're on a budget I doubt you'll really like the costs associated with guides, carnets and visas on this part of your journey. An extra ferry or two won't make much difference in the end.

Similar issues come up a lot along your route through Asia, too. Visa rules change a lot and some are expensive; borders open and close and banditry makes some places awkward. The obvious example concerns what you'll do if you can't enter China? I hope you've looked into this and all the similar issues, and that you and your partner are on the same page.

Hope this helps. Safe journeys!

Mark

PS: your English is excellent! I hope my Spanish is as good someday.