Genre of choice matters a lot - or does it need to cover multiple styles?
How much gain is the amp set for - do you need good strong cleans?
If you need to cover various genres an EQ pedal would make for more versatility, both clean and driven.
There are plenty of cheap and good drive pedals, depending on the flavor you want.
Myself, I might choose two differently voiced ODs that would stack well.
Delay's pretty much a given but if they're sharing power, probably best to go with all analog.
That consideration pretty much rules out reverb.
Choice of modulation (or none) hinges very much on the styles of music.
Same for requiring a gate or not.
For my own tastes a minimalist board for fairly clean amp tone would have low gain drive, high gain drive and delay.
With a crunch core tone I'd do one drive, a chorus and a delay.
As a whole different approach, there are a few Chinese multipedals that contain distortion, reverb and delay.
Add a cheap mini OD of your choice and a multi-modulation pedal that'd cover and you'd be set.
Probably right around $100 not including power and cables.
I've used a Flamma FC-05 that does a good job on chorus, flange, tremolo, vibe, & autowah. Has ring mod and sample/hold filter too.
FWIW, these are not super-robust and longterm reliable - I had to replace mine after less than a year.
I got another when the first one died, though. For just under $40 it does a lot of different things rather well.