I'm another Boss DD-2 player. But most any delay can do slapback pretty easily. I also have a used Digitech DigiDelay that I like as much as the Boss, plus it has different modes. I found it for around $50. on GC online.
i went through dozens of pedals looking for great slapback. none of em were any good to my ears but the cheaper ones were usually better like a vox double dekka. then i bought a pedal i had years ago that few mentioned for slapback. vintage eh deluxe memory man. took about 3 seconds to dial in three or four great slapbacks. all slightly different but all awesome. whatever pedal you get though i found on advice from an old rocker that you stick the delay pedal at the front of your chain, not the back and that works great. before you decide you dont like a certain pedal try it in the front of your pedal chain as well.
I really love my aging Boss DD-3
for slapback on Rockabilly, and some old country tunes...
I like the range in the controls as I know I go for a longer delay time ( perhaps a bit exaggerated) than maybe traditional, but IMO , I just think the sound can be.huge
Aqua puss is great for under $100 used, but if you’re addicted to slap back like me, the strymon deco is special. More expensive, but you also get a great tape-saturation boost, and really beautiful tape flange and chorus sounds (and I usually hate those effects!). I agree with most that say delay pedals are almost indistinguishable from one another when set for slap, but the deco just has this something extra that I find really inspiring when I play.