There are many variables that could affect the answer to such a general question, so let's just hit on the basics.
The power package or drivetrain package consists of a motor, an inverter and a proper gearbox. There is a big range here; basically, the more performance, the more durability and the more range you desire the higher the costs. The range of a proper street legal drivetrain package will run between about $5k and $30k depending. The first or in some cases the second most expensive item is a proper (safe) battery pack. Different end users and certainly different climates and terrains are big factors in both what cell chemistry is right and how big the pack must be. In general, pack cost, not cell cost, will run between $300 and $400 per kWh. Range from a kWh depends on many factors like vehicle weight, climate and driving speed. A small car may get as high as 3 miles per kWh while a class three or four vehicle with a load or towing might be lucky to get 1 mile per kWh and everyone else is somewhere in between. Easy to see that a pack capable of a 100-mile range could cost between $10k and $40k depending on the factors already mentioned.
There are many more components to a complete conversion and then there is the design, CAD, parts fabrication, and maybe powder coating of mounting pieces for all the components. By the time you add everything together along with massive amounts of labor a typical and proper vehicle conversion will cost between $25k and $45k.