An optical packet switch that shares both limited range and full range wavelength converters for contention resolution is proposed with the aim to guarantee a high conversion cost saving. To optimally dimension the number and the conversion range of the wavelength converters, an analytical model, validated by simulation, is introduced. Numerical results show that the proposed switch architecture allows for a conversion cost saving in the order of 90% with respect to a traditional architecture in which only shared full range wavelength converters are used.