And no, before someone asks, you can't just stick newer parts in an old amp and make it louder. Maybe if you robbed the GIANT transformers out of the modern amplifiers and somehow wedged them inside of the old amps you could, but even then, the circuit boards, caps, output drive circuits, power supply drive circuits, etc would ALL need to be upgraded. In the end you might as well have just put the old "Orion" on the shelf and bought a newer amp that already has all those goodies in it.
The price difference these days comes from the fact that all modern car amps are built in China, Korea, or Brazil. Old ones were made in the USA and USA labor is super expensive compared to those other countries labor (wage) rates. Also in other countries it's not illegal to hire school aged children (10-up or so) to work in a "amp factory". Also because of the massive popularity of electronics components (like capacitors and mosfets, etc) the parts cost WAY less than they used to.