You could always buy all the bits and make one yourself, if you know what needs to be done, and how to do it ?
I’ve made a few myself, a couple for a Mk2 GTi and one for my Corrado. If you want to do it properly, it’s not that cheap – some of the eBay looms are really poorly made: non-waterproof fuse holders, basic crimped joints, cheap relays etc. I’d rather do it myself and solder and heat-shrink the connectors etc. Plus you’ll need, at the least, a decent crimping tool, proper waterproof fuse holders, good quality wire etc. The costs soon add up.
Yes, you can do it on the cheap, but do you really want to be driving along with shonky headlight wiring under your bonnet?
It makes a huge difference on older VWs particularly if you also upgrade the bulbs at the same time.