A year extension isn’t massively costly but 2 or 3 years at 180,000 per week adds up!
Even £10m a year cost is relatively good value when you look at the cost of alternatives. You'd have to potentially fid a new striker who's good enough, but would not expect to play every week. He'd then have to fit in and understand how we play. Take an average of Jota, Diaz and Nunez and you're looking at £45m conservatively, as well as at least a £5m per year contract, which is a £14m cost to our bottom line, and also comes with new transfer risk. If the new player was any good you'd be bumping him up a bit after the first couple of years too.
Having access to a top 20 all time goalscorer for us for £10m a year is a bargain. I hate to use a Manc example, but Sheringham was a good option for them either off the bench or for the odd start until around his mid 30's (15 in 29 in the league in the season he turned 35). He then did another 2 seasons with Spurs after that! - Bobby is now pretty much the age Sheringham was when he signed for them, and he went on to play 146 times in 4 seasons scoring 46 goals.
Oddly enough, Sheringhams goals per game for Utd is similar to Bobbys over his career with us. If we could get similar figures out of Bobby, we'd all be made up.
