There is some critical info missing. What i’d need to know, to have an informed opinion, is;
1) Did you make this in the USA?
2) Was your original deliverable a “work-for-hire”?
US rules on work-for-hire mean that you own what you made, but only your client can decide what to do with it, because that’s what they paid for: the right to use it as they saw fit, for a one-time charge. So you’re at a stalemate, unless they agree to let you use the clip differently.
When you make these deals, you HAVE to get them in writing, or the judge is going to default to work-for-hire rules, and rule against you. In writing, when negotiating, you can add modifications like, how long the client can use this for, for how long is their use exclusive, and when does ownership revert to you. You write down the price and when and how it gets paid, and when you deliver the product. Promise me you’ll do that, going forward.
As to your pricing for the clip, it’s whatever the market will bear. Determining that limit is a skill. You also have to weight how “hungry” you are, i.e. are you willing to lower your price a bit to get the exposure now.
Here is a principle I espouse on that: once you are known to have caved-in to a lowball figure, it’s incredibly hard to raise your prices afterwards. Not just with that one client, but every client thereafter, because word gets around. So know what your time and effort are worth, and base your price on a decent day rate, plus a reasonable markup…then you have to be willing to walk away from a number that’s lower. If thy don’t believe you can walk away, they own you.
What one person considers a fair rate may not be based on the same data and circumstances as your own calculations. It’s typical when starting out to look at the competition’s rates for the same level of work, and pick a number that covers your expense plus profit margin, but is also in the upper third of whatever that range is. Negotiate upwards from there.