Quorly — the browser one
Rich text rather than Markdown syntax, no account, and the draft lives in the browser on the device. Free, with PDF and Markdown export included; Pro adds EPUB and sync to your own Google Drive. The trade-off is real: no native iOS or Android app, no library of projects, and sync is something you set up rather than something that happens.
Ulysses — the Apple long-form one
A subscription buys a managed library, goals and publishing to WordPress and Medium. It is Apple-only, so it is not an answer if the Windows or Linux part of iA Writer's pricing is what pushed you away.
Typora — the Markdown one
A one-time licence and a desktop app that renders Markdown as you type. If you liked iA Writer's plain-text files and just wanted a different price or platform, this is the closest swap. There is a full comparison with Quorly if you are deciding between the two.
Obsidian — the linked-notes one
Markdown files in a folder you own, plus a plugin ecosystem. Excellent when the writing is connected to research; heavier than a drafting surface when it is not.
Bear — the Apple notes one
A pleasant Markdown-ish editor for notes and short pieces, with sync as the paid feature. Apple-only, and not built around long manuscripts.