Check Engine light on 1989 SLK 230 Mercedes benz

2 clues: first the low fuel light begins to flash, then the check engine light comes on. Have had a mechanic diagnoise this problem. They replaced the low fuel sensor, diagnostic says fuel pressure problem. $450 later same problem. Any suggestions?

well I fixed it! began thinking about the low octane fuel recently added, & read one of the posts about adding techron or an octane booster. so I tried a bottle of techron. waited 15 minutes, wallah! the check engine light went out. The car Knew! so quick! What gets me is why my mechanic never posed the question about the wrong fuel bieng the problem. Oh well, now Ive got a new $450 low fuel sensor & float assy. Perhaps Ill try a different mechanic. Lets wait & see if it remains fixed! Thanks for the posts about premium vs high octane fuel.