OK, so this I think you should do via CSS only. here is the code:
.pricetag input[type="submit"]{
background: url(../images/icon-plus.png) 5px center no-repeat #F60;
color:#FFF;
padding: 5px;
}
Explanation:
- In Background add the image and color both together
- Set the background position 5px or something to left and center vertically.
- Set the background-repeation to no-repeat.
- Add other CSS as per requirement.
Good Luck!!