I was thinking in my taste, the flat repair cost is difficult early on, and later, you might get red bottles when you could use different colors.

Was going to try it myself, but I wanted your opinion: different recipes which match the theme of each science pack, but then scale up by 25-50x. Red could be burner inserters and, I don't know, furnaces/boilers? Green could be assemblers and underground belts... something different than the normal recipes, but still appropriate for the science pack. Putting in specific ingredients would make the bot produce specific science packs, and help scale the cost of repairing the bots.

That is a good ideia, but then no early bots will be spawned anymore... everyone will always build the lastest one... so.. i dont know...

If you find a science bot early, you'll need red/green, it will be cheap to repair, and would be repairable. A later-game bot would be much more expensive, unusable right then, and take things one can't craft.

Already you can wait to repair a bot... because only getting red/green for 5-10x bots kind-of stinks, and is expensive compared to getting blue/purple/yellow/space