I use Clear & Natural by Metamucil (used to be called 'Free & Clear') , @ 1/2 dosage of Benefiber (1 tsp per dose= 5 grams fiber vs 2 tsp Benefiber) & about the same cost for volume (about $12 for 11.5 oz bottle) so its 1/2 as expensive.
Gabapentin/Neurontin, & Lyrica/pregabalin, as well a pain meds - can be constipating, too.