I’d rather recommend saving a little more money. I see purchasing a mediocre sub as a waste of hard earned money.
In addition to Kew's point, the not-broke but budgeting perspective:
Building the placeholder system, that is serviceable and fits the budget right now. It isn't simply about "saving up", but about priorities.
Sure I could spend more, I could drop $1500 on a sub right now without a problem--but I don't have a clue which one I'd buy, and it would take probably months of shopping to decide--not easily done these days.
Part of building a budget system is about educating yourself, but with low risk: just a few hundred dollars at stake at opposed to hundreds of thousands.
But I won't do that because I am going to buy new doors for every room in the house soon, and build a massive pergola this spring, probably buy a new car, and as soon as covid-19 is beat, we're going to Europe or Hawaii or Tahiti or the Caribbean, etc., then paint the house before fall.
In a few years, when the house remodel is done, and I've bought a couple of Teslas or whatever, got a boat I'm happy with, gone on some epic $10-20k vacations, then I'll drop $10kish on my dream speaker system.
Because then I'll have had time to shop and decide what I like and want.
Until then, I'd like to have something close to reasonably good sound until then. I'm in no rush for perfection, each up grade will be a chance to re-experience music that I love.
Maybe between now and then I'll double up, and switch out gear for $1000kish system, again educating myself.
Heck, if I could've listened to them, I might have 4 Kefs instead of 4 TSIs, might be listening to $4-500 subs right now.
In 5 years or so, I won't care about having spent $160 on a sub for the <$500 worth of speakers I can sell for $2-300 when I replace them with my dream speakers, and in 10 years I won't care about dropping an additional grand on an upgrade.
So, that's why advice of "save and wait," isn't helpful.
That might work for your life, but not for mine, or for many peoples' lives, it seems.