My son's cello isn't expensive I bought it through his school for $1,700.
The A string was about to break so I was looking for replacements strings. Checked a few places new strings for 1/4 size aren't easy to find. At last I bought below which is for 1/2 to 3/4 size and surprisingly it's longer than the original strings by only 35mm.
This is sort of like ink cartridge for printer. Costs of a few sets would exceed the cost of the equipment/instrument. With this and a cello stand for $180 will add to my investment on cello.