Heater cartridges from 3d printers can heat up the aluminium of the engine, if you are able to accomodate a heater block or blind hole.
You get around 40 W out of one. Diameter 6mm and length 20 mm.
No idea if that is useful information, or if i miss the point. At least it is not very expensive (provided you have a power supply already).
Greetings.
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Seeing this reference to 3d printer heaters, I was poking around some sites and noticed numerous sources for hardened steel printer nozzles down to 0.2mm. Very inexpensive. Seems like they might be suitable for injector tips.