I am planning on buying a cheap 3D printer to get into 3D printing, but the printer I'm planning to buy only takes 1.75 mm filament, I was wondering if it might be possible to change the hotend of that printer or something to take in 3.0 mm filament, the reason I want to use 3.0 mm filament is because it is cheaper than 1.75 mm filament.
The printer that I'm planning on buying, on eBay, is this Aluminium-Auto-Leveling-3D-Printer-DIY-KIT-X3A-MK8-Extruder-LCD-2004A-Cover-Box.
First it really depends on your printer / extruder. That said generally 1.75 is cheaper and much more common.
If one were to change the hotend, likely you will need to replace most or all of the hot end. In the case of my personal hot ends, when I did this conversion I had to replace both the tube and the PETF lined mouth. I did not have to replace the tip, core, or the thermsister.
My advice is to pick a different printer. You see 3mm on older extruders like J head direct gear 3-4 years ago and bowden style (like the ultimaker) use 3mm.
Possible yes, advised, no.