Honestly, going ahead and changing to Ada county may, in the end, be drastically cheaper than not making the change and this case going to appeal and retrial.
However, there will be a huge cost to the residents of Moscow if the trial is there. I lived in a city of 100,000 during an infamous national news murder trial and it was frustrating and difficult to say the least. Moscow is much smaller than where I lived with around 26,000 residents. They will experience heavy and slow traffic, full hotels, full short term rentals and full restaurants to the point that locals will have to stand in line for an hour or more to eat out, shortages and long lines in grocery stores, pharmacies, gas stations, and parking problems. In some cases, with this type of situation, the residents have to work from home because they can't get parking near their work and it takes so long to get to work due to traffic and even if they did make it to work, they can't eat out at lunch since it takes so long to get through lines at restaurants but all the single serving foods and bread at the grocery store will be wiped out. And there were some weird things that were wiped out as well, especially in the pharmacies. Unfortunately these infamous cases garner a kind of sideshow with both media and lots of true crime tourism type people coming to try to get a seat in the courtroom or protest or whatever. People who can't get into the courtroom will spend their spare time driving all over town to see significant locations in this case so the traffic will not be only before and after court. While Moscow will make some money from this, it's going to be extremely chaotic and unpleasant for the majority of residents. After my experience, if I lived in Moscow, I would want the trial to be moved or I would go on vacation for the duration of the trial, just to avoid the crowds and chaos that will ensue.