As a cheap offset owner myself, I would advise the UDS route or the WSM if you got the money. My UDS got built for about 75bucks and that counts the new grills and the very used Weber lid, but it did include a ton of my free labor.
Since then the offset has remained a very good grill but I have yet to smoke anything else on it. The UDS will pay for itself within a summer if you used to use charcoal to fuel your offset and you want to smoke stuff weekly(or three times per week in my case)
Pete-my first UDS,a brick pizza WFO, a leaky Chargriller offest, wifes Weber Genesis gasser, and now a Lightening Fast RED Thermapen