define "any good".
define "budget".
to really be able to help you, we'd need to know as much as possible about your intended usage scenario, needs, etc.
required range, speed; required acceleration time from a stop to whatever your cruising speed is.
your weight, terrain you ride (hills, etc), winds, cargo needs, budget, road conditions, etc.
any other info you can provide.
note that any conversion is likely to require making / machining stuff, or paying someone to do that. so, easy will be relative to your skills and tools, or your budget.
regarding costs, batteries are the heart of the system, and usually the most expensive part. skimping on them can disable a build from doing anything near what you need it to. good vehicles / bikes / scooters have good batteries, and can cost a lot because of it. even more if they have a lot of range, especially in a small space.