Which Subwoofer would you choose?

Hello everyone I’m seeking some advice on which subwoofer would be ideal. First off my tv room size is rather large, 20x20 connected to an open kitchen currently I have (2) Klipsch RP280F towers and an Onkyo TX-NR708 receiver, my budget is around $275.00 (Shipped) for a sub I found these 2 subs used locally both in good condition

Velodyne VRP-12 12" $120.00
Velodyne SPL-1500R 15" $275.00

I’m not sure if SPL or VRP is better? or if the prices of these are not worth it? Can I get something better for $275.00? any advice would help! thanks in advance.

I own a Velodyne DD-12.  Their long-term customer support is something less than to be desired. They have simply stopped making replacement amps for many of their earlier model subs, including mine, which was made in 2006. You might ask the sellers of these subs when if ever the amps were replaced and to provide you with proof of same. I plan to get a SVS sub, which has a five year warranty on all parts, including the amp. Compare that warranty with the current skimpy line of Velodyne subs, that offers a really crummy warranty. Maybe you'll be lucky with one of the subs you are looking at, but be careful. 
Either of those subs should "fit the bill".  Please note that the Velodyne company is no longer in the subwoofer business.  If you enter "velodyne.com" into your browser, it takes you to the Velodyne LiDAR website, they apparently are in the driverless car business now.
just bought 2 REL 212 SE subs...trading in an S5. to say they are amazing would be an understatement. The REL rep drove 3 hrs to set them up....free. could not be happier. Any question is answered quickly by their staff.

Actually, Velodyne Acoustics is very much in business in the same location on Digital Drive in Morgan Hill CA.

Their audio related sensor technology has evolved a new company, LiDAR on Hellyer Ave in San Jose CA. for the development of sensors and applications for autonomous navigation and currently provide a variety of these applications to an impressive list of international manufacturers. 

I've owned five Velodyne subwoofers over the years. I currently own two DD Plus subwoofers one purchased new from Velodyne the other used. My only service experience with Velodyne, they replaced the infrared sensor in the used sub out of warrantee for a reasonable price and in less than two days.

I'm guessing they don't offer a product for less than $275. The SPL I owned is still doing duty in a friends home theater.   
Another vote for the Dayton from Parts Express. They are new with warranty and fit your budget. Parts express stands behind their products. I've used several in this line of subs when setting up budget systems and you can't get more for your money. 
I recently looked a several subs for my system and was amazed at the  GoldenEar ForceField 3  which I ended up adding to my system and contemplating adding another.  1000 watts of clean, deep and sharp bass.  I highly recommend new or used.  You will not be disappointed. 
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BK Electronics makes the best consumer subwoofers in the world, as far as I’m concerned. Available to U.S. factory direct from UK. Exceptional prices too. This is the original OEM company which manufactured the ST line for REL and made them famous worldwide.

Take particular note of the Monolith Plus. It uses the Danley designed and Eminence built LAB12 woofer. And 500 watt MOSFET amp. LAB12 is used exclusively in Danley speakers and IMAX theaters and is considered by many to be the best subwoofer in the world.

BK is incredible value and has excellent customer service.
Ditto for the used RELs...I have 2 I rave about here frequently and the first I bought was 200 bucks on Ebay (Q150e 10" front firing 150 watts and it's perfect) maybe 5 or 6 years ago, then a couple of years ago I found a Q108II (8" downfiring 100 watts) in mint condition also 200 bucks...both are superb, reliable things...and sound amazing. I make my own cables from Canare Star Quad wire and Neutrik Speakon plugs...spades are piled together on the speaker posts of my amp, and the main speakers use bananas so no problemo...very highly recommended.
In your price range, you may be able to find a REL Strata . . . They are excellent and great for a music system.  I have one and am extremely pleased with how it works in my 2 channel system!
I'm surprised no one has mentioned JL Audio subwoofers, which I believe are outstanding, quite probably the best -- at any price level, the Gotham (the most expensive), the Fathom (the second-most expensive) and the "e" series.  The subs are quite solid.  they are not boomy, and do not over-emphasize the bass frequencies.  JL Audio, in my humble opinion, and owning 2 e-112's, is the very best.
Look for an SVS 12 " sub used on craigslist so you can audition it before you buy.  Might be able to find an SVS SB-1000 for around $275.  Sells  on Amazon for $500.00.  Google SVS and read the reviews.  A Killer company.
I've had bad luck with used subs. Think I picked up 3 or 4 defectives off craigslist over time. The likelihood that a sub has been over driven and damaged is not insignificant. My policy now is new subs only.
Why are you surprised? Where might one find a JL sub for $275.00?

My opinion might not be relevant here but...…. I have a very high opinion of M&K.. I'm using a restored MX-70B and have never heard deeper or tighter bass. I've auditioned a lot of subs and none come close to it.

Too bad it is no longer the same company...