Resistor pack was £14 plus VAT last time I bought one (2004/05)
It can be fixed for pence using heat sink resistors or standard wire (coiled around a pencil), on hindsight, this is how I would fix but didn't have the info at the time.
Pic is taken from MG-Rover.org, I believe Technozen is your man for getting the heat sinks (Maplins dont stock them anymore??)
The following info is copied from MG-Rover.org into a word doc, have lost the original link......................I take no credit
MG-Rover member - Technozen post 88
With the introduction of the ROHS directive I have found it difficult to obtain some of the resistors that I originally used.
The 3 original MG-R values are as follows...
1.5 ohm 10 watt
0.68 ohm 10 watt
0.27 ohm 10 watt
A single 1.5 ohm 10 watt resistor is relatively easy to get hold of, I have had to use a combination of resistors to achieve the other two values. If you have a similar difficulty you can use the following combinations....
Two 1.2 ohm 7 watt resistors connected in parallel to give 0.6 ohm, close enough to the 0.68 ohm required.
Two 0.47 ohm 7 watt resistors connected in parallel to give 0.235 ohm, close enough to the 0.27 ohm required.
MG-Rover member - Steveguteridge post 95
I'm going to fix mine using Maplin resistors (maplin.co.uk). I reckon the best bet with the values they currently sell is to use 0.22 Ohms, 0.56 Ohms, and 1.65 Ohms (which is achieved by using two 3.3's is parallel). Part numbers H0.22, H0.56, H3R3 (2 off). Total cost is 1 pound plus 2.50 postage (for orders less than 35 pounds). I only actually need the 0.56 one as my other two resistors are intact, but I figure I may as well replace them all while I've got it apart.
With those values speed 4 will be correct (no resistors are used for speed 4), speeds 3 and 2 should come out about 10% too fast, and speed 1 should be pretty well spot on.
I did think about doing it "properly" as Maplin also sell Constantan wire at £5 a reel (4 ohms per metre of wire), but I'm unsure how the power handling varies with the thickness of the wire (the Maplin wire is 28 swg gauge), so I decided against that.