$600 will buy alot of stuff.

for the o2 sensor- ramps ,o2 sensor, o2 socket, sears socket set -all could be bought for $400 with left over $$$.

the od relay probaly needs to be resodered. Sodering is not hard, just read up on it on the web. I just resodered mine and it now works like new. You can buy a sodering gun, soder etc for alot less than $200. I reocated mine from behind the center console to under the glove box.
--
1993 Volvo 245 with a banged up nose