The cheapest option is to have an inkjet and a continuous ink supply system, and buy ink to refill the CISS in 5l containers - brings the cost of printing down to trivial levels. The disadvantage is that it is a certain amount of faff getting it all set up - there's also an initial cost, generally £30 - £40 for the system.
Alternatively, a laser and then refilling toner cartridges isn't quite as cheap but less effort.
You can also do inkjet + refilling cartridges but you have to keep one jump ahead of the manufacturers attempts to stop this - if you google the printer model you're thinking of buying, you'll find out what you need to do to get round their 'expiry date' etc. on the ink cartridges (and how tricky it is).
Our laser printer is a Samsung ML-371x Series PS. We print a fair bit more than you, and it seems pretty reliable. It seems like the cartridges will take 2 -3 refills at least before the quality deteriorates.
If you get a laser printer you can make cartridges last a while longer by once they start printing patchy- take the out and give it a good shake to redistribute the ink particles before each print run (if less than 10or so pages) your printing returns to perfect again. You can get hundreds more sheets out of a cartridge you might have disposed of but a hassle if you need to print more than 10 or so sheets at a time!