Is it worth a back-end developer's time to get into web-design and HTML/CSS
nside: You need to learn it, but you don't need to do it this work. 
First hire a designer.
Then hire a integration shop. Shops like psd2html are doing it for 100$-1k-2k$
So get a good designer and have a shop do the slicing  work.
Then adjust it to your needs..