Radeon 7500, GF2 Ti and GF4 MX420 are all under $60.
Of those the 'best' would depend on your uses.
As a brief comparsion of the abilities:
3D Performance: GF2 Ti is the fastest, followed by the R7500, and the MX420.
Depending upon the application in question the GF2 Ti/R7500 often flip back and forth between which is faster though.
3D feature set: R7500 is slightly better then the GF2 Ti/GF4 MX.
2D Visual quality: R7500 is generally slightly better, GF2/GF4 MX image quality is highly manufacturer dependent.
FSAA implementation: The GF4 MX's is clearly the fastest, but less flexible and slightly blurrier then the SSAA used on the R7500/GF2 Ti.
Anisotropic filtering implementation: The GF4 MX offers the highest visual quality, while the R7500 is generally the fastest.
TV-Out implementation: R7500 is solidly better then the GF2/GF4 which are both identical on the driver level, and hardware implementation is dependent on external TV chip utilized and so will vary between manufacturers.
Multi-Monitor functionality: GF2 lacks it, and GF4/R7500 are very similar in capabilities.
DVD playback quality/performance: The R7500 is a bit better then the GF4 MX420, and the GF2 Ti is clearly inferior to either.
You may want to look into the typical Radeon 9000 which can be had for $66-67.... it is in most respects clearly preferable to any of the above boards and only marginally more expensive.