Webinar series art kit: 12 episodes, $5.40 on Nano Banana, $1.56 GPT

The short answer

A 12-episode webinar series with one 16:9 cover at 2K and three social squares at 1K per episode is 48 images. On Sume that costs $5.40 with Nano Banana 2.1 (12 x ($0.15 + 3 x $0.10) = 12 x $0.45) and $1.56 with GPT Image 2.5 (12 x ($0.055625 + 3 x $0.02475) = 12 x $0.129875 = $1.5585).

Mixing sizes in one campaign is the common case, and the price per image depends on the tier you pick for each asset.

The arithmetic

Covers are shown large and squares are shown small, so the tiers match how the images are used. The per-episode line in the table shows the kit price, and the series line multiplies it by 12.

Using Nano Banana 2.1 at 0.5K for the squares would cut the per-episode price to $0.375, which is $4.50 for the series.

How to run it

Keep one prompt block for the series look and change only the episode topic. Send the first approved cover as an input reference for the rest.

Generate the cover first and the squares after, so the squares can reuse the approved cover as a reference.

Retries and what to watch

The kit is the unit to compare. Nano Banana 2.1 costs $0.45 per episode, GPT Image 2.5 costs $0.129875 per episode, and the Google reference is $0.1512 per episode.

Three levers change the kit price.

• Move the squares to 0.5K on Nano Banana 2.1: the kit falls to $0.375 per episode.
• Move the cover to 1K: the Nano Banana 2.1 kit falls to $0.40 per episode.
• Drop one square per episode: the Nano Banana 2.1 kit falls to $0.35 per episode.

What the docs say to check

Read GET /v1/images/models before you pin a tier or ratio. A model accepts only the values its descriptors list, and the descriptors are the definitive source for what a call may send.

The endpoint pricing lines are what Sume charges your wallet and already include the Sume margin, so a call costs cost_usd times n. Sume bills image generation all or nothing: a generation that fails or is cancelled is not charged.

Google direct is lower than either Sume row for the Nano Banana 2.1 kit, and a little above the GPT Image 2.5 kit on Sume. Pick Sume when the single wallet matters more than the lowest rate.

Every price in this post is a snapshot dated 2026-10-08. The Sume figures come from the public catalog and the Image API docs, the Google figures come from its Gemini API pricing page, and no figure here is a benchmark of quality or speed. Prices and model lists change, so confirm them on the day you spend money.