Why not just use an inexpensive development system with a plug-on A/D board?
All Lawson Labs data acquisition products have three things that you might not know you need. Most competing systems are missing at least one.
1.) True differential high impedance analog inputs. The A/D converter itself will not have particularly high impedance inputs, and may have poor common mode rejection. As soon as you add a differential buffer in front of the A/D converter to meet these requirements, you compromise any internal calibration. Calibration signals really need to come in through the added differential buffer. We do that. It costs a little more, but it is essential for accurate, high impedance differential measurements.
2.) Protected inputs. Our products can survive hard treatment.
3.) Isolation. Isolation breaks ground loops and improves protection.