If you want to use the same DCC signal / voltage as your track then the only ones I know of are Massoth 8FL or Massoth M motor decoder which may be cheaper. I think Zimo do a function decoder as well in their MX68x range, but they and the Massoth are all in the order of £20-£30. The LGB and Massoth single accessory decoders which are designed for point motors primarily can be configured to drive lights instead. They cost a bit more but are already weatherproofed which may be a factor for you depending on where the lights are.
Thanks Dave, the 685 seems hard to find over here, the larger ones are available.... apparently Zimo also makes the MX681, which is 6 outputs instead of 8, perhaps that is even cheaper. Still $28 here, looks like you guys get a better deal over there! I'm moving!
The Massoth 8122302 lighting boards have an additional output. They're available in the US at $35 for a pair of them. That's $17.50 apiece. Set them up so the onboard lights stay off (or just don't turn them on) and use the A2 output. 30mA will not be a problem for them.