One call of the API provides you all LEGO sets ever sold and the average up-to-date market prices achieved in the last 6 month time span as json file for your further processing. Data quality is comparable to Bricklink (world market prices, updated each day and in EUR). One call a week is a good practice to feed your services with current market prices.

Json structure:
……
{
"set_number":"71342-1",
"set_name":"Green Arrow polybag",
"set_year":2016,
"price_new":"14.61",
"sold_sets_new":38,
"price_used":"11.83",
"sold_sets_used":1
},
{
"set_number":"comcon055-1",
"set_name":"Sheriff Deadpool - San Diego Comic-Con 2018 Exclusive",
"set_year":2018,
"price_new":"491.76",
"sold_sets_new":3,
"price_used":"none",
"sold_sets_used":0
},

……