The fixed part is the same whatever the estate is worth: £526 to apply (estates over £5,000) plus £2 per sealed copy. The variable part is whether you pay for professional help. A smaller estate with few assets is usually a straightforward administration, which sits at the lower end of professional fees — and is the most realistic to do yourself. A £100,000 estate is almost always an “excepted estate” with no Inheritance Tax account to submit.
If the estate needs a full IHT400 account, there's far more work — which pushes professional fees toward the higher band.
A house to value, insure and sell or transfer adds time and cost; multiple properties add more.
Each bank, pension or investment provider is a separate set of forms and a separate wait.
A clear will and a few adult beneficiaries is simple; no will, trusts, or minors and missing heirs is not.
For a straightforward estate, doing it yourself for the £532 government cost is realistic for an organised executor.