Trade a SP for a closer?

[RHobbs]

My pitching staff is better than most in the league except for relievers - I'm losing on saves every week. Should I trade a SP for a closer? Which SP should I give up for say a Billy Wagner calibre closer? Please post a link and I'll answer yours. Thanks!

12 Team Yahoo H2H League

H/AB R 1B 2B 3B HR RBI SB K AVG

C V. Martínez
1B D. Ortiz
2B J. Vidro
3B H. Blalock
SS M. Tejada
OF J. Damon
OF S. Green
OF T. Hunter
Util Mi. Sweeney
BN P. Burrell
BN O. Infante

IP, W, CG, SV, HR, K,GIDP, WHIP, ERA
SP J. Peavy
SP J. Beckett
RP Fr. Rodríguez
RP H. Street
P C. Carpenter
P B. Colón
P J. Weaver
BN Bedard
BN U. Urbina
BN Heilman