I agree with Copper_head, Gelert is at the lower end of the market, and although not bad, you can buy better for the money. I'd second Lowe Alpine. I've had my Liberty 70+20 for over ten years, and its still an excellent bit of kit. The link to the Kibo is a really good price as well. Check out Outdoor Magic's Bargain Thread
http://www.outdoorsmagic.com/forum/gear/bargain-alert/7436.html for heads up on kit - you might find a good deal. And sign up for a Cotswold Explorer card - its free, 10% off your first purchase, free catalogue, and you enter a draw each month you buy something. Yes, there are loads of emails, but sometimes a good deal comes up.
Following a tip from OM, found this Berghaus for £72
http://www.gaynors.co.uk/products/clearance/rucksacks/details/i/14001-47esn/n/verden-6510-rucksack.aspx - again, a good solid rucksack for the money.
Copper_head's link to the Berghaus Vulcan was a very good price (although now gone), and if you want to go down the surplus route, try Endicotts. Their grading system is really good, and excellent service. Although they actually do a Gelert pack (the Explorer 65, for £39.99), they might have Vulcan's
http://www.endicotts.co.uk/componen...ps-ii-vulcan-olive-green-1318-detail?Itemid=0 and they have ex-Dutch Army Stings
http://www.endicotts.co.uk/componen...ck-dutch-l-a-sting-d-p-m-2464-detail?Itemid=0 . Designed by Lowe Alpine, and 55L without side pouches, for about £60 you could do well, with perhaps £20 more for a pair of pouches
http://www.endicotts.co.uk/component/virtuemart/bushcraft-on-woods-126/webbing-pouch-side-pocket-british-individual-o-g--1577- detail?Itemid=0
The Stings get great reviews, but give Endicotts a ring and ask them for some guidence. They are really helpful, and won't steer you wrong. Either way, good surplus or decent entry level civvie bag would be fine. Don't go for something thats really cheap - price and value are not the same.