The amount you're willing to spend changes things drastically-
You could get PAX wardrobes from ikea (we have those) and they're quite cheap, decent quality, finance available, and come in variable widths of 50, 75 & 100cm. They're also fully customisable inside and if you want them to be "fitted" it wouldn't take much to put something around them to make them look built in. Fitting into the alcoves in our bedroom they cost £800 and were delivered. They took a few hours to erect with a friend helping me.
I'm currently putting in fitted Welsh dresser style shelves in the alcoves in my living room made of MDF to be painted for their finish. The materials for that, fully finished, will cost around £600. Add in labour for 2 or so days and you're talking the £1,000-£1,200 mark (if you want wardrobes you would add a little more because of the doors).
If you want something made of nice wood sanded and oiled or varnished the materials cost shoots to about £1,500 and labour will be more because the material is harder to work with and takes more to finish (although it looks better). Fitted wardrobes made of solid oak would probably cost you the better part of £2,500-£3,000.
You could always mix and match- if you got the wardrobes made of MDF you can get oak veneer that sticks on like a laminate- so MDF wardrobes with an oak veneer with solid oak doors would cost around £2,000.
These are all guesses- not being a carpenter I don't know what they charge but based on materials cost and an approximate labour cost of £200/day (in London) I think they give you a sense of what the cost might be.