You've already rec'd some really good advice here.

Customizing templates is definitely a highly skilled exercise - you need to have at least a basic understanding of HTML but would do even better with a more well rounded cache of knowledge including PHP (although not totally necessary to make it happen!) and design.

You asked about how much it costs to delegate the customization of a template and there is quite a range, based on the skill and experience of whoever you hire and the complexity of what's being done to the exisitng template - I've seen it invoiced for anywhere from $150 for a simple blog template with just a few tweaks to $500+ for a highly customized template integrated into the existing website's design.

Good luck with your new project!

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