At Q's gym:
Annual fee is $185 regardless of level.
Monthly tuition ranges from $192 (4 hours) - $399 (21 hours).
Booster club assessment, which covers all entry fees, and a portion of travel if airfare is involved, ranges from $315 (L3) to $995 (L10).
So, an annual total of just those fees ranges from $2,804 - $5,968.
This year, competition leo and warmups ran just shy of $275 - same cost for all levels. Leos change fairly regularly (and run around $120 in our gym), though warmups stay the same, so can be worn multiple years as long as they still fit.
So, in the aspect of the "bare minimum", you're looking at (at Q's gym), around $3,000 (L3) to $6,200 (L10).
As someone else pointed out, though - there are many other extras. Open gym fees, specialty class fees, bags, choreographers (as you get into optionals), airfare, hotel, car rental, food on the road, wear and tear on your vehicle, etc.
I think I've said it before, though, that our comparison sport in our family is Hockey. At any given time, one keeps the other sounding reasonable