Most photographers (and I) would say, invest in a top tripod early because its soo important to getting good images. A good tripod could conceivably last you a lifetime. A poor one will need replacing when:
1) You realise how much you need a good one
2) the cheaper one breaks or starts to show wear and tear
3) You'll start to wonder why photos you see in magazines etc are so much sharper than yours
Obviously depends on how into landscape photography you are, what camera you have etc but a good tripod opens up a whole world of night photography and long shutter speeds.
By cheap I mean £20 or less. I own a Slik 340dx, £60ish, sturdy up to about 140cm, you can get reasonably low to the ground with it etc and I have no complaints. Its more of a travel tripod though and will probably be replaced soon.
Have a look
here
for manfrotto, reasonably priced and well made models.
or for Velbon, a popular manufacturer on these boards
Copies of v expensive models can be found on ebay I think but I'm a little nervous to take the plunge.
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