Going down to a 14T front - £25 max gives 1:0.36 ratio front to rear with the 15 / 43 method costing £50 or so ( £125 or so with a good new chain ) running out at 1:0.34
Downside to the 14T front is that if you run plenty of rear ride height the top run of the chain may rub on the top rubbing strip at the pivot end of the swingarm at times - it did when I ran the 14T hence I went 15 / 43 when I had a new chain.