OpenAI tts-1-hd vs Sume TTS: cost for a 150,000-character course
A 150,000-character course costs $2.25 on OpenAI tts-1, $4.50 on tts-1-hd, $7.125 on Sume TTS and $12.00 on ElevenLabs v3. The per-1K math and the job split.
For a 150,000-character course, OpenAI tts-1 costs $2.25, tts-1-hd $4.50, Sume TTS $7.125 and ElevenLabs v3 $12.00. The rates are $15 and $30 per million characters on OpenAI per its pricing page (read 2026-10-04), $0.0475 per 1K characters on Sume, and $0.08 per 1K for v3 on the ElevenLabs API page (read 2026-10-04).
OpenAI's two classic voices are the cheapest per character in this set. The gap to Sume is a few dollars at this size.
| Engine | Per 1K characters | Calculation | Total |
|---|---|---|---|
| OpenAI tts-1 | $0.015 | 150 x $0.015 | $2.25 |
| OpenAI tts-1-hd | $0.030 | 150 x $0.030 | $4.50 |
| Sume TTS | $0.0475 | 150 x $0.0475 | $7.125 |
| ElevenLabs v3 | $0.08 | 150 x $0.08 | $12.00 |
| ElevenLabs v4 (sale to Oct 12) | $0.022 | 150 x $0.022 | $3.30 |
Converting per-million to per-1K
OpenAI quotes tts-1 at $15 per 1M characters, which is $15 / 1,000 = $0.015 per 1K characters; tts-1-hd at $30 is $0.030. Multiplying by 150 thousand characters gives $2.25 and $4.50. Sume's job limit is 20,000 characters, so 150,000 characters is 8 jobs: seven full 20,000-character jobs and one of 10,000, which reserve 7 x $0.95 + $0.475 = $7.125, equal to the single-line total.
Which to pick
- Lowest cost per character: OpenAI tts-1, then tts-1-hd.
- One account for voice, video and image generation with one balance and refunds on failures: Sume, at a premium of $7.125 - $4.50 = $2.625 over tts-1-hd for this course.
- Voice quality is the deciding factor on a course people sit through, so test the same lesson on each engine.
Steps
- Export the script as plain text and count characters including spaces.
- Split it at lesson boundaries so each job stays under the 20,000-character Sume limit.
- Submit one job per lesson and keep the audio URLs together.
- If you want a single file per module, concatenate with a Timeline render at $0.10 per output minute, rounded up.
Per lesson
If the course is 30 lessons of 5,000 characters, each lesson costs 5 x $0.015 = $0.075 on tts-1, $0.15 on tts-1-hd, 5 x $0.0475 = $0.2375 on Sume and 5 x $0.08 = $0.40 on ElevenLabs v3. A rewrite of one lesson costs pennies on any of them, so re-recording is not the deciding factor.
Caveats
Per-character prices exclude any editing, review time or re-records. OpenAI's newer gpt-4o-mini-tts model is priced by tokens ($0.60 in, $12 audio out per 1M), so it is not comparable on this per-character table. Rates were read on 2026-10-04; check each page again before you commit.
Sources
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