The cheapest printer to own and operate may not necessarily be the printer with the cheapest pricetag. As you have already noticed, the cost of ink is ridiculous. That is going to be the main cost of your printing across the life of your printer. Since you already own the Dell printer, can you get cheap ink refills? That may be the easiest way to go with the least investment for you.
Because you mentioned you are primarily interested in B&W printing, I suggest you consider a laser printer. The purchase price will be higher, and the cost of the toner cartridges will floor you, but the cost per page (paper not included) is in the 1 cent range. An inkjet cost will be in the 4 cent range for B&W text. Roughly that translates into saving $150.00 on ink/toner per box of paper (5000 pages.) Plus you are going to replace almost 9 inkjet cartridges for every toner cartridge.
As far as speed goes, I have found a laser printer to be consistantly faster than an inkjet even though they may be rated at the same ppm rate, I think the inkjet printer people are a bit optimistic. Also, there is less/no smudging with a laser printer and imo the printing looks sharper.
I know that didnt help you narrow down your choices. Just dont go so cheap it ends up costing you more money in the end.