We experienced the same thing. The cost of moving is high because you have been on their platform for years. The cost of staying is high because of the price increases. Either choice feels bad.

We decided to move in the end to our self-built platform [1]. As a software company we had the experience to do it: the application development, the infrastructure... It still took a lot of work.

We opened it to the public some time ago, and people seem to like it. We hope to have enough people on the platform one day so it is self-sustaining. At the moment it's a cost that we willingly pay to have something that works well for our own business. Staying would have been cheaper in the end, but this one is more fun.

EDIT: feel free to let us know if something important is missing for you. We are open to suggestions. The current plan is to add invoicing next (including peppol integration).

[1] https://www.abejora.com