If you owned the property as 'joint tenants' then the property doesn't form part of your partner's estate. You now automatically own the whole property.
https://www.gov.uk/joint-property-ownership
If you owned the property as 'tenants in common' then, if your partner left a will, the provisions of his will apply. (If he left his half of the property to you then there's no reason why you should pay anyone anything).
If you were tenants in common but your partner died intestate then the rules on intestacy apply:
https://www.gov.uk/inherits-someone-dies-without-will
Whoever now owns that half of the house can invite you to buy that share or can seek a court order forcing the sale of the property.
However if you and your partner were living together in the property for 2 years prior to his death as husband and wife (or as civil partners if you're male) you're entitled to apply to a court to vary the provisions of your partner's will (or to vary the rules on intestacy, as appropriate) on the grounds that the will (or intestacy rules) failed to make reasonable financial provision for you.
https://www.legislation.gov.uk/ukpga/1975/63
So you might be able to get some, or all, of your partner's share in the property awarded to you. (You'd definitely need legal advice if you were considering going down that route).
Assuming though that you and your partner were tenants in common, that he didn't leave his half of the property to you in his will and that you don't intend to apply to a court to vary the provisions of his will (or to vary the intestacy rules), then it would not be unreasonable of whomever owns the other half of the property to invite you to purchase their half. It's not clear from your post though what the relationship, if any, is between that person (or group of persons) and the executors. It's ultimately up to the beneficiary/ies of the other half of the property to decide what they want to do with it, not the executors.
It seems perfectly reasonable though that you should want to see the valuation of the property before entering into any financial arrangement. However, if the beneficiary/ies of the other half of the property (or the executors acting on their behalf) don't want to cooperate, the simplest solution for you is to approach a local estate agent to get a free valuation on the property for yourself.