How far into your Diploma are you? Most Uni's will offer students the opportunity to ''upgrade'' to the degree after 2 years if your grades are good enough.
If this isnt an option, you could try evening classes, I did several modules towards my degree this way at my local uni, I think they cost around £250/module, already having a diploma you would have to do I think 8 of these, @2 years and £2000. I think you'd have to wait till after you qualify to do this but Im not sure.
Many uni's also offer these modules via distance learning so you can easily do themwhilst you work once youve qualified.
Hope this helps,all this from someone who never actually got around to finishing their degree!!
(waving to you from sunny scotland)