Here's one selling for $60:
Features
Robust housing.
Large LCD display.
Reading: .01" / .1mm / 1/64ths
Accuracy: .01" / .1mm / 1/64ths
Length of arms: 4"
Spring loaded with locking nut.
Battery: CR2032
Here's one with better accuracy; it costs more than a bore gauge
:
Minimum Measurement (Decimal Inch)
0.3750
Maximum Measurement (Decimal Inch)
1.3750
Graduation (Decimal Inch)
0.0010
Accuracy (mm)
0.0380
Accuracy (Decimal Inch)
0.0015