Well 300 for a clutch master cylinder to me is ridiculous because I just bought a new one for 100 bucks OEM, and it take about 20 min to install including bleeding the line. The rubbery feel could be due to air in the line so either bleed the system yourself (I can give you a run down) or take it back and have them rebleed it. If this doesnt solve it, then you may be looking at a worn out clutch.