Add a "30davgprice" value or "7davgprice" value to the tradeprice API. It would just be the average price of that resource over the last 7 and 30 days.
Double commas in All-Cities API! Currently I can see 15 of these... We shouldn't have to fix your invalid JSON in our code.
Instead of a hard-coded 5s or so delay in the tradeprice API, have it return data from 5s ago instead. Or even better, remove the delay altogether, it's honestly more annoying than useful for preventing against scripted trades (P&W market doesn't change quickly enough for 5s delay to be effective IMO)
...and please fix the data types, you shouldn't be storing numbers as strings in your DB anyway.