It is the cost of the upkeep, either the infills or repairs. I used to have acrylic nails done in a salon but the cost just got ridiculous. It needed doing every 2 weeks.
Now I do my own at home with an acrylic dip powder, (resin painted on, dip in powder, spray an activator) but you have to be good at filing both left and right handed. Shaping the side walls, the top and then the thickness of the acrylic on the nail.
Shellac/CND nail is a cured nail polish where you do not file the natural nail plate, but you need to soak it off to remove it every time you have the nails done.
Gel nails are like acrylics but they use a gel on a brush that is painted onto the nail, again you have to soak them off to remove them, or they can be filed down and just the growth area refilled.
Acrylic is a monomer liquid you dip a brush into then into acrylic powder and this is applied to the nail. Again to remove them they have to be soaked off, or filed down and infilled.
The filing down is because the nail needs "re-balancing" because the acrylic is shaped to be thin at the cuticle then thickens up the nail.
The short answer is you need to consider upkeep if you go down the fake nail route. 
And if anyone is interested in seeing a pro do nails, then Nail Career Education is a fantastic watch here