I like a sub for HT - even a somewhat lumpy one. You want some air displacement for booms which is hard for bookshelf speakers.
That's basically what JLM said. But in my own experience, when you get the booms called for by the program material, you also get some unwanted booms and thuds and bass trash where there shouldn't really be any, which for me, detracts from the overall experience.
I like a sub for HT too, but not in the context of this budget. I haven't heard much I like under $500. Well, except maybe for my
dual Celestion 8s that just barely make the grade.
Maybe the $569 Rythmik L12 could be added to the budget a bit down the road after he has been bitten by the good sound bug!
Steve