What’s a 2nd hand Brompton L5 folding bike worth?

It is a 1999 model with front pannier... where can I sell it and much should I sell it for?

You could try seling it for free at Craigslist.org or start up an ebay sellers account with a credit card and pay a very small fee to sell it on ebay.com, also try listing it in Yahoo! classifieds!

I’ve compares some prices on folding bikes for you and was not able to come up with a price for your brand but other folding bikes on ebay are priced from $50.00 for electrics to about $350.00 for a new Hummer brand but bidding is still open on those