37 event posters: 2 low drafts each, then Pro 2K finals, $8.77

The short answer

Drafting 37 event posters twice each on GPT Image 2.5 low at 1K and finishing every one on Nano Banana Pro at 2K costs $8.77 on Sume: $1.83 for 74 drafts plus $6.94 for 37 finals. Running all 37 on Pro at 2K with no drafts costs $6.94, and all 37 on GPT Image 2.5 medium at 2K costs $2.06.

The draft pass is cheap enough that it mostly decides one thing: whether the layout and the wording of the headline are right before you pay for the finishing model.

The arithmetic

Sume bills the catalog row times n, so a draft is 1 x $0.02475 and a final is 1 x $0.1875. Rows are the default-option prices read from the public catalog on 2026-10-08. GPT Image 2.5 is tiered by quality and size, so the low 1K row and the medium 2K row are different prices of the same model.

The totals below are computed from those rows, not rounded up front.

What the draft pass buys

The drafts add $1.83 on top of the finals, which is 26 percent of the finals bill. That is the price of seeing two layouts per event before committing. If your poster briefs are stable, skip the pass and the plan collapses to the $6.94 line.

One thing to keep in mind: a draft on one model and a final on another will not match composition. The draft tells you whether the idea works. It does not preview the finished pixels, so treat the Pro render as a fresh image from the same prompt.

Sizing the poster call

Posters are portrait. Nano Banana Pro lists 3:4 and 2:3 in its aspect set, and GPT Image 2.5 lists 3:4 as well. Send aspect_ratio explicitly. The Pro 1K and 2K rows are the same price, so there is no saving in dropping a Pro poster to 1K; take the 2K.

Each call returns Sume-hosted URLs. A call that runs past the 30-second sync budget returns a 202 job envelope, and you read the images from the job result. See the Image API for the status-code rule, and Jobs and results for polling.

When to change the plan

If a finalist needs 4K for print, Pro at 4K is $0.375. Swapping 5 of the 37 finals to 4K adds 5 x ($0.375 - $0.1875) = $0.94. Failed generations are not billed, so a retry after a failure costs nothing extra.

Check usage.cost on the first response of each model before you launch the full run, and compare it with the row you budgeted.

Handling revisions and a client sign-off

Event posters change late. Date, venue and sponsor lines get edited after the first draft is approved, and a text change means a new final. Budget one revision for a share of the set: if 12 of the 37 posters get one more Pro 2K render, that is 12 x $0.1875 = $2.25, taking the plan to $11.02.

Keep the draft round for layout and the headline, and keep copy edits for the finishing model. A GPT Image 2.5 low render is a cheap way to test whether a long headline fits a 3:4 frame, but its output is not what the client signs. Hold back the finals until the text is frozen and you avoid paying the higher row twice.

Because Sume bills only completed generations, a final that fails at the provider costs nothing, and you can resubmit it with the same prompt. Record the job id of each approved poster so you can match the billed amount to the poster later.