The cost varies on the tools.
The audio and music are free. The music requires you request access from Google, but they grant pretty easily. I had to do a little editing on the music to make it loop properly.
You can get free image generation, but I paid for Runpod.io servers with Stable Diffusion Automatic1111, which are amazingly easy to set up. They charge about 35c per hour and a 512x512 image takes 2s to generate. I use the background remover tool, which makes it take about 12s per image, but I just let it run while I code and then come back to browse the image gallery of 20 images for the one I like. I also used a bit of ControlNet on Scuba Steph to get the poses. There was cleanup on a number of the images needed, and I did some compositing on Scuba Steph.
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Thanks for the reply. By the way, I recorded a video where I play your game among other games. If you interested to see that start around minute 34:00 https://youtu.be/rrcP1iedi5E?si=34O4aE06oUQHqi9F