Don't know about Viagra.
If cost is the issue, try Sam's Club Pharmacy.
Husband had a couple of prescriptions that were both around $150 at Walgreens, AFTER what insurance pays.
Checked at Sam's Club, both around $45 there. So he gets those filled at Sam's.
If a tablet is scored you can split it, even in quarters, but use a pill splitter. But if in doubt, ask the pharmacist.
No pill splitter gives 100% accurate 50/50 of the medicine. One half will contain a tad less of the medicine than the other half.
Often this small difference is of little to no consequence.
Splitting into quarters of a tablet will have the same effect.
The more times split, the more inaccuracy in dose delivered.
As TsuDoNihm said, if the instructions say do not split, then DO NOT split.
Often these are extended release (ER), delayed release (XR), etc. for a specific therapeutic effect.
Splitting these types will negate the desired effect, and very possibly do some harm.