Agree with a lot of the comments already made. Here is my take.

How much will they pay? As mentioned, this will depend on not only the value you are generating today but how much value will your business provide when combined with theirs. It could also help if there is another business willing to buy your business. It may pay to find another potential buyer as it can ratchet up your business value quite alot.

At such an early stage multiples mean very little. It all depends on how much you are willing to sell it for. If this number is worlds apart from what they are willing to pay then its probably not worth wasting time discussing further. The amount can be affected by the terms of the deal. For example, whether its all cash or you earn equity in the merged company as well. If the latter potential upside could be significant so you dont necessarily need to get the big number up front. This model has many pros and cons and requires a lot of advice on contract terms particularly regarding control and commitment to investment.

Finally there was a recent acquisition I am aware of where the seller worked out a valuation based on how the buyer's company was valued. This is easy if the buying company is public, not so easy if the company is private and hasn't had any recent investment. But if possible and favourable it could be a great metric to use.

Hope that helps and feel free to call me to discuss further.