It depends on what you class as lightweight but in my opinion the best ground level tripod around the £100 mark is the Manfrotto 055XProB.
i bought this one awhile back on offer from here
http://www.amazon.co.uk/gp/product/...m=A3P5ROKL5A1OLE&pf_rd_r=1S93VXDQTKH5J6CTJR64
i find it very good and has the movable column for near ground shots, just a little over your budget
A friend of mine has one of these and, for the money, it is a cracking piece of kit - she paid 80 quid without a head.
Before you decide have a look on the used market. I was patient and picked up a Gitzo 3 series Carbon systematic with a rapid center column for 100 pounds! I thought the shop wanted 100 pounds for the center column (which was a bargain!) but that was what they wanted for the whole kit (about 400 on E Bay at the time) so it pays to look!