Welcome to Apple Discussions, Mark.
As Matt has said, I paid approximately £50 (£45+VAT) for an Apple Authorised Service Provider,
Hi-Tec, to install a 100GB 7200RPM Hitachi Travelstar into my PowerBook. The drive was sourced online from
http://www.lowestonweb.com at the lowest price I could find (without trying ebay). The same drive is now available for around £130, although smaller capacities (ie. a 7200RPM 60GB), will be around £100.
However, if you are happy with a smaller and slower drive (ie. 5400RPM 60GB) then you can expect to pay under £60. So, potentially, the repair could cost around £100-110 or less if you replace the drive yourself - but you should be careful that you are totally confident about doing the job.
As for the MacBook Pro... I agree with Matt. Wait for a rev. B or C model. My current 15" PB is a 1.25GHz rev. A and there have been plenty of times when I really wish I could have waited (but, at the time, work dictated my buying decision).
15" 1.25GHz/12" 1GHz PBs, PPC Mac minis, 12" iBooks G3/G4, Mac OS X (10.4.5) Cube, TAMs, iPods 2G/4G, iPs, AEBS, AX