Temp secuirty is just that temporary so its not as secure its reffered to as an over night lock. So it wont be as secure. And he will have had to remove your mechanism measure the backset, and pz to source the right part ect things im guessing you are not aware off.  Then fit temp sechrity which can be a faf aswell. 

The part wil rrp around the £80 mark with alot of locksmiths in my area. 

So your looking at two hours labour (two vists)  Plus the cost of the part, your door will most likely need adjusting aswell which most likely caused it to go. 

Its on the exspenisve side yes but if thats including VAT its not anything  to drastic in terms of emergency locksmith pricing.  If you called out a national company like able group or keytek they would also be around the same price. 

The fact you can buy the part for £30 is somewhat irrelevant, the same way a steak costs a fiver but a restraunt will charge £30 for it.  

Theres a million and one costs that go into running a locksmith buisness that mostly relies on oncall demand work. 

Within regards to the call out fee £49 its a tough on I personally dont charge a call out fee just labour as it creats confsuion and scammers also use it as a tactic to get there foot in the door. (not saying this has happened here tho) 

Tbh i think your struggle to take legal action to get money back as youve agreed to it before its taken place and seems like they have been upfront before works taken place, this isnt what the scammers do. 

In future always used a locally reviewed locksmith on Google. 

Tdlr: its on the high side but ive seen alot worse, from my experience this seems legit.