The 'Bass' Argument

In case you aren't on Facebook and hadn't heard, my nearly 13 year old wants a subwoofer for his birthday. In fine teenager form, he sent me an e-mail explaining why he should have a subwoofer. Here it is, exactly as written.

"Hi mom i know that you aren't sure about me getting a sub woofer here are some reasons i want one and here is a link to the one i want.
http://www.svsound.com/products-sub-box-10nsd.cfm
Oh and I will pay half of the sub woofer plus you can charge me interest if you want to. I want it because I am so addicted to bass and my speakers just don't deliver enough bass for me. I have heard dads sub woofer and realize that even his small one has better bass than my speakers. Plus with a sub woofer and bass speakers i will have the ultimate bass system but don't worry I will not play them if you ask me not to or will at least turn them down [after I argue why not to turn them down or off]. Uncle Andrew is going to get me a bunch of bass mekanik stuff [or he said he would and I wached him look for it] so that will sound just plane great with the sub woofer. I know for a fact that you like bass to so I don't think you would mind it too much. I will also play it a lot when your gone so that it absolutely can't bother you. I know what your thinking by now "oh i thought he wanted a PSP really bad why does he want this too. All he thinks about is buy buy buy." Well i do think about buy buy buy all the time but you know doesn't everybody for example dad is always talking about how he wants stuff for bikes and drums and racing and I know you agree. Also you always want clothes and technology [like phones and computers and laptops for example]. Also I know that I wanted a PSP but you know I have thought about it and I think that video games are not that important any more because skateboarding and stuff like that is just as fun or more fun plus you get exercise. As I have said before I love love love low and loud bass so I think I need a sub woofer for bass mekanik and other stuff plus rob zombie has some good base [in fact one of there songs has a low whistle that goes really low and you can almost feel it in your nerves]. Well now you know thatI i need and want a sub woofer for my birthday and remember I will pay half and you can charge watever amount of interest you want [within a resonable range like 1-30$ a month].

And there you have it. Nevermind that the sub he wants is $400 and we already have one "average" sub in the house, which he has been monopolizing for some time now. The "interest" thing is because he doesn't actually have the cash to pay half until he has spent the spring/summer mowing lawns. I doubt we would charge him, but I'm glad he understands that aspect of borrowing money.

My brother (the above-mentioned Uncle Andrew) is a self-described "bass snob" and sub-20Hz aficionado, suggested the SVS. While I know SVS would be a fantastic way to go, it's seeming to be more than we want to spend on a birthday present, even if our son does pay for some of it himself.

Do any of you audiophiles out there have a recommendation for a bit more "moderately" priced sub that will satisfy a 13 year old for a few years, but still deliver nice bass?