If you are looking for a rocket that is simple to build goes to extreme altitudes and is cheap grab a T Bolt.
here it is with the fincan already made for you glued in place and the bell nozzle retainer already in place.
here we have it with the rail gides on and the shock cord mount in place (you cant see it) it is a simple build you can do in an 1/2hour if it wasnt for glue dring times there is nothing hard about it.
should do around 10000ft on a J350
but it will need a tracker as this will be an easy lose in the confriguration i have it in main at apogee
yes i am crazy but i have a tracker.
will post another pic when painted.