In reply to 2E0YYY:
The materials alone would probably cost way over £25. Traders are
asking six quid for a dipole centre these days!
Well, each to his or her own - I bought a SOTAbeam 2/70 when I was getting back into amateur radio, but have built all my antennas subsequently. There’s no need to buy a dipole centre for a home-brew antenna.
B and Q stock 6mm raw aluminium tube (don’t use the anodised version) for about £2.50 for a 1m length. It’s easy enough to extend this to a bit over 1m for the reflector by using a bit of steel screw to add on an offcut from a director!
They also stock plastic tube, which I use as the dipole centre, with the dipole elements a tight push fit. (I’ve used 8mm tube for the dipole.)
A 3m length of 21.5mm overflow pipe for the boom costs a few pounds (just found it online at about £3 inc VAT). If you need something collapsible, that pipe fits neatly into black electrical conduit; use a 40mm screw to hold them together.
You need a few rubber grommets to hold the elements centrally in the boom. For the dipole feed, drill 4mm holes through plastic and metal to take 4mm plugs. Or put screws through and attach croc clips as with the SOTAbeam (though if you use screws you then need to take one screw out to disassemble the antenna).
Use a balun of some kind (even the choke type as for the SOTAbeam) on the feeder.
Certainly not “way over £25” but under £25 - and I’ve found the DK7ZB designs great. My DK7ZB 7-ele for 2m has a boom that’s 3.3m long though, which is a bit much for SOTA - I normally prefer to take my DK7ZB 5-ele which has a 1.5m boom. Cheaper too!
I find the 7-ele a bit “pointy” for SOTA use, though it’s nice to have the extra gain for contests - but it’s not that much more gain than the 5-ele (less than 3db - half an S point!) which is why it doesn’t go out a lot. The extra length is also more of a nuisance especially in a wind.
None of these designs for short Yagis (and the 3m boom is a short Yagi!) have a huge gain over a dipole of course - the 5-ele DK7ZB is 8.5dB better than a dipole. However I like to have a bit more gain and a bit more directivity than a dipole for SSB.
The best bit for me is the satisfaction in using something you’ve built yourself. I know that’s not everyone’s cup of tea but it’s the way I enjoy my amateur radio. A great hobby with room for all ways of doing things.
Good luck with the new antenna anyway!