If you want to save money in the long run buy a compressor or spare rear wheel. Then manage your good, part worn and well worn tyres to suit what you, the weather and venue are doing.
Had 1 new IRc and 1 new Xlite this year and still both in ok condition and have ridden 3 S3s, 10 Normandales, 2 Welsh champs numerous centre hard, evening and esay trials and a fair few practice sessions.