Sometimes dogs just get intestinal upsets which can be fixed easily, and can be attempted to clear up at home as long as the dog is acting fairly normal otherwise, non-painful, not pale, not dizzy, no longer vomiting, and eventually will eat. If it doesn't clear up at home, then a vet appointment is necessary, as antibiotics or deworming or just something to settle the GI tract may be needed. Also, although watery stool and straining is common with diarrhea, sometimes a partial foreign body ingestion can cause this and it's very important to keep a good eye on him the next couple of days to make sure there is continued improvement.
Do continue to offer water if he'll drink. (If not, he can always have some unflavored pedialyte). Try offering a bland diet like boiled chicken or boiled hamburger meat with white rice (1:1 ratio). No treats, and don't let him eat grass either. Continue this diet for a couple of days as the stool firms up. Once firmed up, gradually go back to the regular diet over the course of a few meals. Usually they will attempt this type of diet after some time if not forced.
If needed to get him more settled and to start eating, you could also give Immodium (loperamide), which dosing information found here:
Make sure it has been 12 hours since you gave that pepto, and don't continue pepto, as it contains aspirin properties and can lead to stomach ulcers and thus feeling sicker with continued vomiting. Try this, and if not clearing up in a couple of days, you'll want to make a vet appointment then, or if looking worse by tomorrow, seek a vet sooner.
Best of luck, and let me know if I can help further.
I wouldn't go more than 24 hours without forcing small amounts of liquids if refusing to eat or drink anything, and at that point, if not perking up within a couple of hours from then, I'd seek vet attention then, just to avoid dehydration and more severe problems. If he sarts to drink but doesn't want that bland diet, and if still acting normally, 48 hours is ok IF he is indeed taking in some fluids.
There's no way of knowing what brought this on without knowing exact cause (GI upset, parasites, etc). Usually it is just the way food was eaten or just an off day for digestion, like people get at times, but without testing you can't be sure.
I'm sure he was fine at the vet visit. A lot can change in 24 hours, let alone 2 weeks, especially with GI issues. Costs vary greatly depending on individual clinic and part of the country, so there's no way of me knowing hoq much the clinic you are going to would charge and what diagnostics may be needed depending on how he's doing at that particular moment. Unfortunately giving you what my clinic charges won't be helpful, as we are among one of the most expensive in NY State, and often 2-5x's more than most other hospitals.
You have every right to call and ask the physical exam/ office charge in advance, and once there, a printed estimate of charges which you can deny or agree to, pick and choose what can be done, and know exact price up front.