I'll do a quick calculation for you below.
I managed to pick up a Sparco seat for like RM500, about 90 quid
The profile was quite cheap as I sourced it from a local supplier.
4080
1500X2pcs-RM240
420X3pcs-RM100.80
500X2pcs-RM80
4040
420X1pc-RM21
500X2pcs-RM50
250X2pcs-RM25
300X2pcs-RM30
200X2pcs-RM20
*Total-RM566.80*
Needed some extra profile and some 90 degree aluminium angle connectors
4080
2 x 600mm 4080-RM114
1 x 500mm 4080-RM47.50
4040
1 x 500mm 4040-RM34
1 x 420mm 4040-RM28.60
12 x slim L brackets 4040-RM84
TOTAL-RM308.10
4040 Angle BracketX16-RM112
4040X420MM-RM28.60
Nut+Screw(M5/M6)X2-RM6
Total-RM146.60
So far approx RM1500, (£300) for the bulk of the rig, just the 90 degree angle code brackets, t-slot nuts and bolts that I sourced from online retailers in China.
Will try and find them and advise cost shortly