Depends on what's needed, but on the Sea Fury, I've used two sizes, 0.3mm and 0.4mm, to replicate the different hose and pipe sizes. These are available from 'Plus Model', in gauges from 0.2mm to 1 mm, rising in sizes 0,2. 0.3. 0.4 etc.. There are around 20 to 25 lengths in a packet, each one being at least 6 inches or more in length, and the 0.3mm cost £1.25 per packet.
The company also supply lead foil, ideal for seat belts and other 'fabric' type requirements. Of course, if you need just one size for everything, say 0.5mm, then a reel of lead solder might work out cheaper, but for the price of the Plus Model stuff, readily available at my LHS, it saved having to search out solder in the right sizes.