Not as easy a conversion as you think, easier to build a new boat.
Was going to convert mine to a 2s setup, new or re-drilled sponsons, move the boom tube in the tub accordingly, this is to fit a battery, then move the radio box bulkhead as it interferes with getting everything back far enough to get the cg right.
was figuring 2s 5000mah 40c packs, Swordfish 200 esc with a Leopard 2860 4050kv 1300 watt motor max vs 1000 watt max for a 540xl. I don't like running an esc near it's limit hence the 200 amp esc.
Not exactly budget but also not top notch but still well over 150$ before you get into props, thats after a complete rebuild on the boat.
Still planning to build do one electric but it will be purpose built from the start to fit everything properly.