Calculate total price with 'WITH RECURSIVE'

I have a table 'Leistung' (which means activity in english) and one for the match between two activitys with a given amount (benoetigt). So for example the activity with the ID 2 needs three activitys with the ID 3.

Each activity (leistung) has a price.

I now wanna calculate the total price for all activitys (leistung) including the price from the child activitys in the right amount.

Here are my tables with some testdata:

CREATE TABLE Leistung (
  lnr INTEGER PRIMARY KEY,
  bezeichnung VARCHAR(100) NOT NULL,
  price NUMERIC(7,2) NOT NULL
);

CREATE TABLE benoetigt (
  lnr INTEGER REFERENCES Leistung(lnr),
  benoetigt_lnr INTEGER REFERENCES Leistung(lnr),
  amount INTEGER NOT NULL,
  PRIMARY KEY (lnr,benoetigt_lnr)
);

INSERT INTO Leistung(lnr, bezeichnung, price) VALUES
  (1, 'Discokugel', 100),
  (2, 'Strobolicht', 100),
  (3, 'Verstärker', 90),
  (4, 'Gelaender',50),
  (5, 'Bühne',50),
  (6, 'Bühnenelement',20),
  (7, 'Stromverteiler', 40),
  (8, 'Stromkabel', 20);

INSERT INTO benoetigt (lnr, benoetigt_lnr, amount) VALUES
  (5,6,12),
  (1,7,1),
  (2,7,1),
  (7,8,1);

I am pretty shure that the solution only works with a 'WITH RECURSIV' query. My first attempt ist this:

WITH RECURSIVE benoetigtlist(lnr,benoetigt_lnr,menge) AS (
  SELECT lnr, benoetigt_lnr, menge FROM benoetigt
    UNION ALL
  SELECT  b.lnr, b.benoetigt_lnr, b.menge
  FROM benoetigtlist bl, benoetigt b
  WHERE b.lnr = bl.benoetigt_lnr
)
SELECT * FROM benoetigtlist;

But i don't know how i can make the link between this result with the pricing from the activitys.

Or is this the wrong attempt?

Here is a SQL Fiddle from the testdata for better understanding: SQL Fiddle

EDIT: The desired output is a list with all activitys with the total price, including the price of their children.

For the testdata above the result should look like:

id  text          price
1  'Discokugel'     160  // 100 + 1*40 + 1*20
2  'Strobolicht'    160  // 100 + 1*40 + 1*20
3  'Verstärker'      90
4  'Gelaender'       50
5  'Bühne'          290  // 50 + 12*20  
6  'Bühnenelement'   20
7  'Stromverteiler'  60  // 40 + 1*20
8  'Stromkabel'      20

For example the activity with the ID 5 'Bühne' has a total price of 290, because the activity intself costs 50. Also this activity needs twelf activitys of ID 6 (which costs 20) (according to the first entry in 'benoetigt').

In summary: 50 + 12*20 = 290

In the as duplicate marked question the recursion only happens in one table. But i have the problem that the price information is in another table.