Firstly, welcome to the forums! Envira is currently not available, but I'm in charge for all current requests, hope that's alright. You came to the right place to order your custom theme.
Our services start at $50 for a basic theme and the price increases depending on the complexity of the theme. Features such as CSS-only buttons, custom navigation and other various features are considered to be 'advanced' and therefore you have to pay more than the starting price to get them incorporated into your requested theme.
If you provide us with more information on what kind of theme you're looking for (apart from the forum niche), when we'll be able to provide you with a proper quote. We'd also appreciate if you could specify what kind of budget you have available for us to work with, just in case you don't have a clear vision of how your theme should look like.
Thanks for considering MySkins for your them request!