hi
having just changed my alternator 14 days or so ago ...dealer was a nightmare keep supplying the wrong parts ..since you mentioned the tensioner i guess you have aircon like me ..all in for parts alternator ,belt and i did my tensioner .was a personal choice ...came to £300..i gave up on my discount to get the parts the following day VOR ..so you should get them cheaper if you are prepared to wait a couple of days if they aren't in stock ......if the garage who is doing the repairs supply and fit ,they will add a mark up to the parts ,and as previously stated there is the cost of discharging and recharging the aircon ,roughly 30 mins ..so you are looking in the region of £400 plus though you may get about a £40 surcharge back for the old alternator ..i recommend you supply the parts yourself ,will be cheaper