Top most affordable HMI SCADA software platforms

These SCADA programs from GE and Rockwell etc can cost an arm and a leg. Especially with add-ons and upsells. For smaller control systems, worth looking at:
1) Nucleus Command Systems (flat rate pricing, no limit on data).
2) Ignition (basic package is affordable but doesnt include a lot of features)
3) VTSCADA (good for bigger systems with more costs and complexities)