Try to join instead of using nested correlated subqueries:
SELECT spendings.id, spendings.price, spendings.title,
dates.date, users.username, currencies.value,
y.sum_price
FROM spendings, dates, users, currencies
JOIN (
SELECT day, SUM(sum_table.price) As sum_price
FROM (
SELECT day(d.date) As day,
s.price
FROM spendings s, dates d
WHERE s.date_id = d.id
AND day(d.date) = 25
LIMIT 2 OFFSET 0
) sum_table
GROUP BY day
) y
ON y.day = day(dates.date)
WHERE spendings.date_id = dates.id
-- AND day(dates.date) = 25 <== commented since it's redundant now
AND spendings.user_id = users.id
AND spendings.curr_id = currencies.id
Some remarks:
Using old join syntax with commas is not recommended: FROM table1,table2,table2 WHERE
The recommended way of expressing joins is "new" ANSI SQL join syntax:
FROM table1
[left|right|cross|[full] outer|natural] JOIN table2 {ON|USING} join_condition1
[left|right|cross|[full] outer|natural] JOIN table3 {ON|USING} join_condition2
....
Actually this "new syntax" is quite old now, since is has been published, as I remember, in 1992 - 22 years ago. In IT industry 22 years is like 22 ages.