Inclined to disagree, with the all out spend if available option, even if you had unlimited budget, and everyone else had unlimited budget, there's still only so far you need to take it on the initial spend, in my eyes the following features are a bare minimum for any buy:
isis
oversize bars
proper trials freewheel/freehub (or space in your budget to allow one, tensile ffw is mindblowing value...
sealed hubs/more sealed bearings as the spend increases...
trials bikes are delightfully simple, and as far as buying parts go, they're like AK47's for compatibility, unlike mtb and road bikes where owning one brand of shifter will define your choice of mechs and you can be tied into buying things a certain way forever without spending a huge amount to make drastic changes, trials gear all fits and works nicely most of the time, and the bikes in my experience on a whole are pretty reliable/cheap to maintain. and i don't disagree with a comprehensive initial investment to make sure the bulk of the bike is good to go for a good stint of time with no surprises.
looks likes you can't buy a complete 26" from tarty thats in any way bad or unsuitable for purpose anymore, and the blade is a mad bargain you'd be silly to spend less than that on a 20" for new or you'll spend over the odds when upgrading it in the long run, unless you're heartfelt sure trials is the most important thing you need in your life where spending £1200 on a sturdy high end bike not a SL comp machine is a great idea/investment...
TLDR:
if going second hand
ISIS
oversize bars
sealed hubs (rear at minimum)
proper trials freehub/freewheel
if new, £650 for a mod with a decent enough spec to not give you any nasty suprises. (actually a pretty respectable achievement if you consider what a good mtb costs nowadays...)#
and 26"s don't exist for just shy of £999, (is this purely cause onza don't have anything out other than a high end 26" where is the 26" BLADE? or any reasonably decent 26" frame for under £200?