Really Giant Problem

for information we have done all design with paint.net It’s not very good but it’s very easy to use

I would also look at http://www.gameart2d.com/

They offer some freebies and some of those are UI elements that you can use for a lot of buttons. For making your own:

Adobe Photoshop – as low as $10/month with their Photographer Bundle or part of the $50/mo full Creative Cloud suite. or $20/month single app. (raster)

Adobe Illustrator – $20/month single app, $50/month full suite. (vector)

TheGimp – free (raster)

InkScape – free (vector)

Paintstorm Studio - $25 one time, raster

Autodesk Sketchbook Pro $5 / month, $30 / year (raster) <---- really good drawing tool.

Adobe Fireworks, which allowed for both raster and vector images in the same environment, has been discontinued by Adobe.  However, I’ve found a great replacement.

Sketch (free trial / $99)

It has a great workflow and I used it quickly generate all the sample art for my Dynamic Shader demo