Does anyone understand yet, if only the 5-bux slot increases its price after every droid? Will the price be reset if you use another slot? Maybe it's more reasonable to just move onto the 15-bux slot and try to get the level faster than in the 5-bux slot?
The "free" slot will increase every time you use it. At some point, it becomes worth it to spend the bux on the 15-bux level. From my observations, the 15- and 25-bux levels don't increase in price. The price remained constant after I forced a rescan, so maybe the price comes down after the normal rescan time (that hasn't happened yet, so I don't know this for sure).
Edit After the free droid timer reset, I can confirm the price goes back down to 5 bux.