Depends on room size and volume.I don't agree on that. To get the high range to very good level takes multiple thousands minimum. You may get entry level sound super cheap but very good? Forget it.
Converting a bedroom into a theater could be done cheap, converting a basement is going to cost a bit more. Still spending over 35k on stuff, especially with used JBL equipment the expense is marginalized, build your own subwoofers and it got a lot cheaper.
There's nothing magical about what equipment a theater uses, they just use a lot more of it because of the bigger room. What they do that most don't know about is professional level EQ. It's not as simple as buying some over priced pre-processor and some more over priced amplifiers. If you don't EQ your room forget about theater like quality.