My question is does it matter which of the two methods are used as far as value goes? I just cant figure out why the price range is so drastic except possibly for that.
You aren't missing anything, it's exactly that simple. Correctly done G36 conversions are plastic weld jobs done by TommyBuilt Tactical. Those conversions cost more to complete, and hold their value better as a result.
As for the final price you expect to pay, well that can differ dramatically based on the configuration you want. This is another reason why you see such a huge range of prices. You have the G36E, G36K and G36C as the most popular models. Then on each there are different fore-end, rail, and sight/optic options. This will drastically change the final price based on what you pick.
If you are just starting now it could be difficult to build one on any relative budget. The donor HK SL8 has been out of production for several years now and as such the prices have been steadily increasing. You could easily pay $2500-3000 just for the donor rifle before any parts or labor. Beware, and run all the numbers before starting.
Short story, min price is probably around $4500 and you can easily bump that up to $6000 depending on config.
Here is my G36C built by TommyBuilt. Good luck!