Small Wire:

28 AWG Stranded $4.50 per 10 feet each Black and Red
Small, flexible.

30 AWG Stranded $6.90 per 10 feet each Black and Red
Fits tight spaces where some flexing is required.

36 AWG magnet wire $4.50 per 10 feet each Red, Green, Yellow, Blue
When run up the inside of a signal bridge leg and painted it just disapears.