Where are you getting the $100k from? I would guess that a control system, communication system, reaction control system, propellant, batteries, solar panels, and a camera would cost much more than that if you're designing it to withstand space. The Indian probe you mentioned was 15 kg and cost $24 million. If you normalize that down you're talking $1.6 million per kg for a mission notable for its low cost. The LRO cost $504 million total, and Atlas V costs around 230 million If we take $250 million to be conservative, then it cost $2.5 million per kg of scientific instruments.
Note that the Indian orbiter had a dry mass of 500 kg and a launch mass of 1,337 kg to support that payload. The LRO has a dry mass of 1,018 kg and a launch mass of 1,916 kg. So the LRO had 10 kg of supporting dry mass for every 1 kg of science, and the indian orbiter had about 30 kg of supporting dry mass for 1 kg of science. Lets add Kaguya as another data point that had 1,984 kg dry mass, 2,914 kg launch mass, and the mission payload seemed to be around 300 kg, for a ratio of 6 kg weight for 1 kg of science. In other words, as your satellite gets smaller, the weight of all the other stuff required to keep your satellite ticking and pointing in the right direction becomes dominant. That means that one satellite with 100 kg payload will likely have less total weight than 50 satellites with a 2 kg payload. That increased total weight will come from installing redundant systems on all your satellites. So we're talking higher launch costs and higher part costs. Its certainly going to be difficult to improve upon costs by a literal order of magnitude.
So then the question becomes, what science can we accomplish with 50 satellites that we can't with 1? Is there a benefit to all this added cost and complexity?