Neither of mine wore DJs, there were some who did but by no means all. DS1 wore a grey fashion suit from Next. Lovely but never worn again. DS2 wore a black suit (not DJ) with red waistcoat and dress shirt. He has worn the suit a lot since but has now outgrown it. The boys all dressed very smartly but not all the same.
Yes have a look at what they wore last year. My DS' school last year, more in smart suits rather than DJs, though a mix. Mine had a lovely 3-piece suit from Next and a glossy silk tie chosen by his little sis. He looked gorgeous, I think the trs and jacket may come in useful again - or maybe not (he's no taller but getting more muscular) - but bet we'll spend more on DD when its her turn anyway, so not too fussed