EL34 equivalent tube types

I've had a Coincident Dynamo 34SE sitting around for my bedroom system, and I just on a lark decided to hook it to my main system for some 100% tube/analog listening sessions. I'm actually amazed at the sound this 8 watt amp is putting out.  Right now it's equipped with the (I believe) stock EL34 tubes (from tubedepot). Just looking around, vintage tubes seem to be extremely expensive, but are there equivalent drop in replacements that I could be looking at? Just to play around with, nothing serious.

This is also making me consider a more powerful tube integrated (my speaker makes recommend at least 30 wpc tube amps), but similar topics already exist so I wont create another thread for it.