Why do lithium batteries vary so much in price?
The 100Ah battery from your question has 4 cells in series, each one having 100Ah capacity working at or around 3V. This makes a 100Ah, 12V battery that can hold 1200Wh (watt-hours) of energy. It is the energy that makes the price (and mass, and volume) of a battery. You get ~0.8 USD per watt-hour.
Rather on the expensive side, but still normal (at least here in EU, you can get comparable product for ~5 USD per ampere-hour at 12V).
The 24Ah battery is (persumably) single cell of 24Ah (or multiple cells in parallel that are together 24Ah). Its working voltage is like 3.7V (the chemistry is slightly different from the above). It holds 24 * 3.7 = 88.8 Wh for USD 40.00 or like 0.45 USD per watt-hour. Cheaper than the above, but probably pretty much low-grade (both in cycle life and safety) and/or less than the advertized capacity.
And, assuming they are of the same quality, to get them comparable to the first battery, you will need not 4, but rather 12 of them ($480) and it will be up to you to get a sane battery management (probably another $100-$250) and mount and connect them safely (whatever $$$). And because of the different chemistry, they will never be as safe as LiFePO4.