You should be able to do the conveyance for a few hundred. You might even fancy doing it yourself since the risks associated with getting something wrong arent necessarily that high and you’d learn something.
monthly rental multiple of 60 implies a yield of 20% 1/(60/12) which I would call a bit soft. and be looking closer to a monthly multiple of 100+. But it will depend on the quality of the fabric of the building, any service charge or ground rent payable and of course the local market.
I have done lots of valuations around TJ’s figures in London before. Surprisingly expensive luxury, a garage.
If your local rents really are closer to £30 per month, then Id budget 30*12*(1/15%) = £2,400 + £100 if you do searches and land registry stuff yourself, or a few more £100s if you pay a solicitor.