I tend to use https://www.hopandgrape.co.uk/
They have a good selection and are pretty reasonably priced. They often have sale items too its well worth checking regularly I've had some bargains from there. It depends on what you're actually after buying on who is the cheapest? And what sort of gear you're after of course. I have friends that have spent exhorbanate sums on the most basic of kit, after all a 5 gallon bucket it a 5 gallon bucket. Helps to buy smart if you're on a budget
For equipment check gumtree. The amount of stuff on there super cheap or even free from "tried it once" brewers is amazing. Pressure barrels and fermenting buckets are on alot, I've even gotten them for free! (well in exchange for a few bottles )
The cheapest I've found for extract as well and the hops are brilliant.
Whats good about the extract there is that it comes in 3.5kg batches(LME) as apposed to the usual 1.5 (3kg). You always end up 500ml short for any recipe I've looked at and he seems to be the only person who's realised this.