The cost of a lease extension can can very much depend on your freeholder. You may have a very reasonable freeholder that will quote you the market rate. More often that not this doesn''t happen. Freeholders are well aware that your ability to sell you flat is diminished with a short leases compared to a lease that is in excess of 125 years. Coupled with the fact that the valuation on your flat will also be less that a flat with a long lease. in some cases you will not be able to agree a figure and you will have no alternative to ask the Leasehold Valuation Tribunal (LVT) to decide on the price for the extension.
It is not uncommon for a freeholder to ask the full price of a lease extension plus £5,000 - £10,000 which is what it will cost you if you decide to go the the LVT because you will be liable to pay for all of the costs. If you are unable to agree a price with the freeholder and you go down the LVT route the costs can build up very quickly. You will be liable for both parties costs which you should consider. These can include solicitors fees, surveys, and expert opinions.
On the other hand if your freeholder is reasonable and does not ask for an excessive premium you will be able to agree a price and put the solicitors to work. In most cases you will have to pay for the legal costs for the landlord but you won''t have have the costs involved with the LVT