Used bike with 20" Wheels. 6'3" is near the 6' 4" limit for Dahons, - first step is to go to your local Halfords, bike shop, or folding bike shop and try a few for size. Then lurk on here, Ebay, and Gumtree. Used Downtubes are good for tall peeps., but only appear rarely in the UK although Velo Chocolate now import new ones.

Check out Winstanleys Bikes (Wigan) in their clearance section as there's often 25% off 2008 bikes. Fudges, in the Harrow Road London, are good on Dahons and Bromptons, and do discounts on last years models. My local Halfords has knocked 50% off a new 2009 Mu. Shop around but spring is the most expensive time to buy, and decent used bikes are rare or overpriced.

At £300 if you can go to that you are well in the region of a close-out 'new' Dahon Speed D7 or Vitesse D7 or a Mu. Ebay can be good but competition for used folders is high, and there's often a better deal on a 2008/2009 bike from a dealer. As you're tall, check there's enough knee room twixt you and handlebars, especially on 16" wheel bikes, unless it's a Brompton.

My 2009 Vitesse D7 was new at Christmas from Fudges: £300.00 but VAT increases and seasonal re-pricing has increased that by 10%. The similar 2008/2009 Speed D7, a very capable steel-frame folder is a little cheaper if you shop around. Most of the UK folder dealers now sell on Ebay too. There are a handful of UK folder die-hards on here too, they occasionally upgrade and sell bikes here, or at least notify when they are on Ebay.

Further down range is the estimable Dahon/Raliegh Boardwalk, which should be smack in your budget if the bike fits you. They are well regarded.

http://www.fudgescyclestore.com/index.php?p=74070

The Giant Halfway is getting good reviews, as do the more expensive Mezzo's which I've ridden and thought were good. Mezzos often appear in half-price close-outs. Bromptons can only be had for large wads of cash.

At the very bottom of the market are the 'no-name' £100.00 Chinese folders on Ebay. I did run one of these last year, but the build quality was not in the same league as the cheapest Dahon and I was very unhappy with it. One exception is the 'Kent' magnesium folders which are cheap, and have a good reputation for frame sturdiness although components are 'low-end'. I haven't seen a 20" version for a while though. The Halfords 'Apollo' folders are of reasonable quality, but not overly specified, and often it's only another £100 to get a well- specced bike, which will pay off in the long run - you won't feel the need to upgrade in six month's time as components corrode or wear.

If your employer is part of the 'Cycle to Work Scheme' there are tax breaks and monthly payment schemes to be had.

Bear in mind, once you even sit on a folder you will be sucked into a maelstrom of desire and savage mania for folding bicycles which will never leave you. Tread warily my friend, it's a slippery path towards a life of incurable obsession.

Whatever you get, a rear rack is good, and you'll need tyre levers, a dog-bone spanner, a pump, and a spare tube. A saddle/seat bag to keep them all in is a good idea. A helmet, many feel, is a wise investment.