Tubes are a gamble. They can last 10 minutes or 75 years. Who knows? It all depends on how hard you push them and what quality they are. A 4 pack of power tubes would set you back just over 100$ and preamp tubes are about 7$ each. Yes they are easy to change, pull old ones out, push new ones in.

You have to look around the price a bit and say, "look what I'll be getting for a few more dollars". Get the DSL man, They are a great amp and sound awesome with a Les Paul.