A sniper robot would be workable with off-the-shelf technology. You could hide it in plain sight by simply making it look like a city garbage can or a vending machine.
The problem with static, low-cost technology is ingress and egress: whatever the mission, the idea is that there are no pieces for anybody to find once it's over. Ideally the robot would move itself into position and get the heck out of dodge with a high degree of invisibility. That's why man-portable UAVs work so well. Heck, we're already using them for reconnaissance. (But you're right about the technology problems. Only a few countries could mount such an effort)
The problem with static, low-cost technology is ingress and egress: whatever the mission, the idea is that there are no pieces for anybody to find once it's over. Ideally the robot would move itself into position and get the heck out of dodge with a high degree of invisibility. That's why man-portable UAVs work so well. Heck, we're already using them for reconnaissance. (But you're right about the technology problems. Only a few countries could mount such an effort)