Ikea units are relatively cheap, and really good quality, but I think Boobies has the right idea. Standard carcases, then doors from somewhere else (probably Ebay Shops.)
Ebay shops for the appliances as well. Go for simple, plain tiles or the budget will be shot. Also, with a tight budget, try and do without all the silly cornice/plinth things if possible. They mark the prices well up. I often do painted kitchens, so I tend to make a lot of the trim up from standard timber. That may not be to your liking though.
I've just been fitting a Homebase kitchen. Very good, but crazy prices for fiddly bits such as monster self-closing pan drawers. I think this 2-drawer unit alone was over £700. With a standard carcase and drawer packs from someone like Screwfix, you could save a lot.
Just to give you an idea on fitting .... this kitchen, including tiling, will be around £1700. Homebase wanted over £3000.