eBay for jackets. Pay as much as you can afford - ie if you can afford £100 get a bargain less than half price Showing Selection / Mrs Candy / Alexander James.
Don't skimp on your hat, buy new and buy good - if you fall off showing you still land on the same bit of your body as you would falling off XC, its not worth the risk.
USe yellow dusters to dye cheap white shirts and breeches canary.
Visit charity shops for ties, and often waistcoats.
Ditto Loopylozzas above comment
doesnt have to cost a fortune, i show on a budget aswel
- of this whole outfit, the MOST expensive bit (at the point/cost that I bought it) was the £40 bespoke browband. Saddle excluded!
Jacket £5 (car boot- £300 hunt coat!), boots free, shirt £3 tesco, tie £2 charity shop, breeches £20 eBay.