errmm
Wessie....
RE: "Toner units are £60 but you should be able to refill afew times before quality goes off"
sorry to sound dumb here but what do you mean by 'quality goes off'
do you not just change the toner cartridge when it is empty? or does the drum get damaged?
sorry- I know absolutely zero about laser printers )

obviously!
I used to work for Xerox and the object of the printer game is to sell you proprietary consumables.
On larger photocopiers/printers the toner is added by the user as required. A bottle of toner every 3000 A4 prints maybe. Kerching. The print cartridges, which contain either a drum or belt, are designed to last for many thousands of prints. 30,000 is typical for your average A3 copier as found in the corner of a public library. At Xerox we fitted a device to the cartridge so that the customer had to replace the unit after 30,000 copies. On early models it was a fusible link, on later models it was software controlled. On the slave machines used for testing electronics I used to override these devices and the print cartridges lasted for hundreds of thousands of prints (although not at optimum quality).
On smaller SO/HO printers the toner/drum module is a sealed unit. Once the toner is exhausted you are supposed to replace the whole module. It's analogous to inkjets: the manufacturer sells the printer relatively cheaply and makes their money on consumables. Kerching. You are usually encouraged to return these units so they can be refurbished and sold back to you. They are supposed to tell you the unit is refurbished but you'd be surprised how many refurbished print cartridges found their way into the printers rolling off the production line...
With my Samsung printer, the toner/drum unit is designed to give you 3000 A4 prints before running out of toner. Samsung would like you to buy a new module for 60 quid but it has a nice rubber bung in it and they have not installed a crippling device. You simply remove the bung and add toner. As this unit is electromechanical it will eventually wear out. I reckon you should be able to refill it at least twice before noticing any degradation.
With the more expensive ML3561 printer, designed to work in an office and claiming a duty cycle of 150,000 prints a month, the print units will last up to 6000 A4 prints with 5% coverage. 12,000 prints in economy mode. Spec here:
http://www.samsung.com/uk/business/...hite/ml-3561n_and_ml-3561nd_(and_ml-3560).htm
Toner refill kits are widely available on the web or just go along to your nearest Cartridge Express shop. It costs about £15 to get it done for my little printer.
Googling brings up this page from the US, specific to the ML356x:
http://www.ink-refills-ink.com/printer/ML+3561+ND/12809/
It appears Samsung have fitted a crippling device to the module in the ML356x series of printers. This vendor can supply the toner and electronics to overcome this. At 10 dollars the electronics is not going to be very sophisticated and may just be replacing a fusible link with a blob of solder.
So, before buying your printer, do some research. Work out how many prints a month you will do and understand the possible consumable cost as this is likely to be many times the purchase cost of the printer. Check to see if non-branded consumables such as toner refill kits are available. If possible buy a printer that has a duty cycle considerably more than your requirement: running any printer at the margins of its capability is rarely a sound economic prospect. Also, if your business expands you will not need to upgrade immediately.