The cables are available on eBay for reasonable(ish) prices, but the adapters are kind of expensive. Your choices are basically buying a used NI/Agilent PCI or USB adapter, buying a Chinese Agilent clone or buying the Prologix adapters. Expect to pay about $100 for an Agilent clone, about $150 for a Prologix GPIB-USB and a bit more for a genuine NI/Agilent GPIB-USB. PCI adapters tend to be cheaper since they are less versatile (will not work in laptops or some modern desktops).
Either you can find some existing software that supports your device, like the Agilent/Keysight Intuilink / BenchVue software, or third-party software (like the
KE5FX software), or you will have to develop your own software. Popular software development environments include NI Labview, EZGPIB and many programming languages with VISA bindings. Commercial software will generally not support the Prologix stuff, but some hobbyist software (like the KE5FX stuff and EZGPIB) will. I am guessing the Lecroy update software would only support NI adapters, but Agilent and Agilent clones may also work.