I reckon domain.io is exactly what you're looking for. It's the best option I've found, at least, even when I'm not using their landers - it's worth it just to have everything in one place, and to be able to ensure everything is listed correctly at dan/afternic/sedo at a glance.
You'll be looking at $12/mo for under 100 domains. If you use Domain.io's landers/nameservers and get a sale via Afternic/Dan/Godaddy, the 25% commission is rough. But if you're using domain.io's landers/ns, and you get a sale via the lander, you can import it into dan and only pay 5% commission, so it can go either way.
I'm using Dan's landers right now (Rather just get the 15% than roll the dice on 5-25%), but still using domain.io to manage my portfolio.
A really nice aspect of using domain.io's nameservers, however, is that you can add your verification codes for various marketplaces so anytime you get a new domain, just switch to the domain.io nameservers and you're all set without having to manully add txt records and all that.
If i recall correctly, the hope initially was that they'd integrate directly into the major marketplaces to keep your portfolio and prices up to date. Instead, you'll have to just quickly export a spreadsheet with your names + prices (and you can have it automatically adjust the prices by a % for each marketplace, if you'd like to charge more on higher-commission platforms).
I don't want to sound like a shill, but I just finished getting my 200ish names all organized finally, ensuring they're all listed in my accounts on each marketplace, no straggler listings from previous owners, etc - came here and saw this thread.
I think it's kind of a backburner project for the owner at the moment so there isn't much in terms of new features, the support is a bit slow, but I've never had to reach out for anything urgent.
Just hoping they don't sell get bought by Godaddy anytime soon (: