Grahm.
First of all yes 72 quid IS a bit high for a repro, especially when you can get a repro (like this one) from Shiperfrabrik for 25.00.
However, the military DID issue these full kilt aprons, the biggest problem was that kilts were very pricey, yet at this time still purchased by the war department. So, the aprons were used to help preserve the kilt. Also, another complaint was that during the winter, the bottom edge would freeze and then start to actually cut into the bare legs, so once again the kilt apron hung down PAST the bottom of the kilt to try and combat this.
Here is a picture of a group of soldiers from the LIverpool Scottish WWI. Also notice how high some of these lads are wearing the kilt, AND the braces being worn with them.
Cheers,
Chad