There is a reason why 'Himalayas' & 'Argos' are not often in the same sentence...
Seriously, I'd get something better.Much better. Your spending a fair amount of money
http://www.theguardian.com/travel/2013/may/24/trekking-in-the-himalayas-nepal-everest just getting there, and you want to get the best out of the experience - that tent is possibly just about suitable for a festival (its even got the word 'festival' on it)in the UK, August, if there isn't much rain (and popup's are a PITA anyway). And its camo - possibly not a good idea in Nepal.
Head over to Outdoor Magic to ask for some suggestions.If rg598 is right, and 3/4 season kit might be usable, perhaps something like the Zephros or a tent from the Force 10 range? Personally, I'd want something as tough as the Alpkit Zhota (down to £350), but its got to work in possibly lots of different conditions, and be relatively light. Thats going to be nearer a £100 tent. See what you can borrow - you never know.
There are a couple of kit lists here:
http://himalaya-alpine.com/about-us/travel-information/himalaya-trekking-gear-list/ &
http://www.acethehimalaya.com/desti...rna-base-camp-and-tent-peak.html?op=Equipment
As far as the sleeping bag, again, get the best you can reasonably afford. Being cold is just horrible, and being cold where you've got the same problem for at least a week or more is much worse. Remember you've got to carry your kit, and the mantra is: 'you can have it cheap, you can have it durable, and you can have it light - chose any two'.
You don't need to spend a fortune, and it depends on the sort of conditions you expect to have. This came up on a thread on OM a while back about a bag for Everest Base camp, where someone asked a similar question
http://www.outdoorsmagic.com/forum/gear/-12-sleeping-bag/28041.html - and someone said they had used a £50 bag usually bought by cadets. My reaction was that the person had been lucky not to freeze their n**s off, and the bag was really heavy. For synthetic (assuming down is out of contention on budget grounds), something like the Mountain Hardware Lamina 0 might do well - currently £145 but hunt around for deals, etc. Thats the sort of level I'd be looking at. As you'll see in the thread, someone suggests renting a bag - thats a good idea, since for much the same price as buying a rubbish bag, you can rent a good one. Spme companies sell off ex-hire bags as well
http://www.expeditionkithire.co.uk/stock-for-sale.html
Think about £110-150, to be realistic. For about £150ish, you might get a really good deal on down bags, like this one
http://www.climbers-shop.com/10899040/products/rab_ascent_700_xl_sleeping_bag_special_offer.aspx
Joe Brown has the same price (and they both have the very decent Rab 900 for £165 - more base camp than foothills, but good kit). Synthetic is going to be heavier, but dont spend less than £100ish - your just going to end up with something which weighs a ton, or is really cold, or both. The extra £50 you might spend is probably how much you'd be willing to spend an hour if it gets really cold and your bag isn't warm enough. Although I dont think my Snugpak has ever been as warm as it should be, you could do well with something like the Crysalis 5 - about £89 on the net in some places
http://www.outdoorgb.com/p/Snugpak_Chrysalis_5_Sleeping_Bag/, and while bulky, gets decent reviews
http://www.mudandroutes.com/archives/reviews/snugpack-winter-sleeping-bag-review
Frankly, its really an Osprey 12, just not green.
Check out Outdoor Magic's Bargain thread, since all sorts of deals come up, and their sales pages. Ebay isn't a bad bet, but check online prices first. Just because its on Ebay doesn't mean its going to be cheap. There is also the fabled Rab factory shop, and use things like the 10% you get off the first time you use the Cotswold EXplorer card (which free), and all those weekend only flash sales.
Dont forget a decent sleeping mat, it can really help. Alpkit arn't doing any at the moment, but something decent and light will mean a warmer nights sleep.
There is a thread about Everest Base Camp here:
http://www.outdoorsmagic.com/forum/travel/kit-for-everest-base-camp-trek/9444.html - which might be useful.
The kit your taking is critical - you've got to rely on it, and if it doesn't perform, your going to be very uncomfortable, at best, so its worth paying a bit more and spending more time researching and looking for the stuff that will do the job, so that you get the best out of the trip.
I can't help with spiritual enlightenment, but hopefully you'll sleep well, not carry too much on your back, and really enjoy it - and of course come back safe and well!