Hi Carl
How much is it for these tubs,
You can get various suitable tupperware containers from Asda from well under a fiver. Drill/punch some holes in the lid and that's it job done
Buy a chunk of bark from a reptile place (£5 for a big bit) and a bag of Irish Peat Moss (£3) or maybe Vermiculite (£2) as the substrate.
If you have a larger spider then 9"x9"x12" fish tanks cost about £9 from all garden centres and so on. Again, a few holes in the lif and put a book or something on top to stop the spider pushing it off. For deep burrowers and arboreals (tree tarantulas) custom tanks are available from around £10 - the £15 size is big enough for any adult. Also pet shops sell plastic "pet pal" tanks with snap on ventilated lids for under a tenner. Very cheap and easy but I don't personally like plastic as it dulls and scratches with time.
and what size would be good for a begginer
If you buy a spiderling it will be cheap, but very small and often fragile. Adults are pricey, but easy to care for - but you don't know how old they are.
Best bet is to buy a sub-adult (ie 3-4") female from a reputable breeder, or at a show - NOT from a pet shop as the vast majority are overprice and underinformed
That way you get a tarantula that will live at least 8 years (up to 30 in some species) Males only live a couple of years, but if you get a male don't panic because he can be "studded out" to other females, and you will get a share of any resulting babies
How much does this all cost - food as stated.
For one spider, a single box of crickets a month is more than enough (£2.50). In fact, most of these will probably go to waste.
I keep 70 something tarantulas, and still only go through a box a week, various sizes of course. If you have hundreds/thousands you can get bulk deals on crickets.
Not really, they aren't intelligent enough. Some people report tarantulas becoming "used" to being held, but in all honesty handling is not advisable as most are easily spooked and may fall to their deaths. For instance, the one in the pics I just posted ran up my arm, over my shoulders and down my other arm. An easy situation to lose control of, resulting in a nervy and possibly wounded spider, and maybe even a bite (normally in self-defence)
A lot of people don't realise just how fragile they can be.
Could someone explain the humidity a bit more?
It's not as crucial as many people think. As long as the soil is reasonably moist (ie it doesn't turn into a dust storm when you blow on it) then things should be just fine. Humidity gets over-emphasised in the same way that people tell you to not EVER EVER look near the sun....it's just better safe than sorry