Ed this went from a simple circuit to a sub-panel which is most certainly the way to go if you are a good distance from the main panel. It will probably save you money in the long run if you find you need more circuits later. Make sure the panel has room for any desired additional circuits you may later want to add. Also be sure the amp load is sufficient to handle the highest running load you can imagine in you shop at one time. That's key, what is the total load at one time.
For most of us that's a power tool and at least lights, and a dust collection system. Leave room for your wildest hope of an upgrade or you'll possibly be looking to do this again. Be sure you check local codes for your location and national codes also play in. SER/SEU is almost always aluminum but some places do carry a copper SE cable. Key there is very tight connections on the lug and using the electrical paste. You'll have two choices, main lug and main breaker. The main breaker is the safest way in that you can kill power to all the circuits by shutting off the main breaker.
Otherwise if there is a fair distance, or dictated by electrical code, you may need/want to install a disconnect to feed the panel otherwise you'd need to kill the breaker feeding the sub panel from the main panel. In as many jobs as I have worked I've never seen copper going to the sub-panel.
But with all this said, unless you really know what you're doing, know electrical code/have reliable (not here) knowledge I strongly suggest at least consulting an electrician and do check with your city/county building division for the need of permits and inspections. If it is required and you don't go this route you leave yourself wide open to negated insurance claims should they arise as well as possible action by your locality.