As with most things in life- you get what you pay for.
Yes Stihl parts are DEAR- but they are usually also the best quality.
Oregon used to make some nice clutch kits for most popular saws and that would perhaps be the next step down or similar to OEM quality.
Cheap Asian clutches are usually (and somewhat surprisingly) not that bad- IF it were not for their weak springs. OEM springs fir Asian clutches though.
Sprockets- again, Oregon is cheaper but near as good as original- Asian ones work, but usually wear faster- so can be false economy as they need replaced more often.
Bars? Well the World is your oyster there- more choices than you can point a finger at- usually once again, price will dictate quality and laminated bars with fixed nose sprockets will always be cheaper than solid bars with replaceable tips.
Get the correct pitch, gauge and bar mount sorted and make your choices. Personally I have found Sugi Hara bars here to be of good quality and miles cheaper- but thats where I live.