Well, since it is a Squire, you may want to try getting this project done without your mods being worth more than the guitar. The rail pickups by GFS are one option as stated, but here's another from GFS if you want an overwound single coil that retains a little more of that single coil tone.
http://store.guitarfetish.com/provalstpiou.html
I would normally reccommend CTS pots for replacements, but in keeping with the budget minded theme, these ALPHA pots are a good choice.
http://store.guitarfetish.com/fusi50aupoal.html
Again, my normal reccomendation regarding ohm rating for the pots would be 250k, but these pickups are seriously over-wound...in humbucker territory by resistance rating.
Since I like to wire my strats with a tone control on the neck and bridge pickups with the middle wide open, these are the caps I personally would use: 716P, 200 v Orange Drops - .010mf for the neck, and .022mf for the bridge. Although it's traditional that a Strat middle and neck tone pot share the same cap (usually a .022mf on modern Strats), It's only a few cents more and a little extra soldering (very little) to give yourself two distinctly different cap options that are more tailored to the individual pickups.
I'd replace the 5-way switch with a CRL for under $10.00, and replace the input jack with a Switchcraft for under $3.00.
Many folks like the locking tuners, but they can really add to the cost of your mods very significantly. Although I do have one Strat clone with Sperzel locking tuners, I've had just as much luck using good non-locking tuners and a good post wrap, personally. You should be able to find a good set of Gotohs or Grovers for under $35.00. If you're patient, you can even find a new/pulled set of Fender American std. tuners on Ebay at a reasonable price (I think they're made by Shaller if I'm not mistaken).
So, with these basic mods, you're looking at less than $120.00 plus shipping. If you want to go the extra mile, I'd recommend replacing the bridge as well with one that has a steel tremolo block. IMHO, the tone difference is too significant not to, but now you're talking about adding at least another $35.00- over $100.00. If one of the Callaham steel blocks will fit your bridge, that is an option as well.
I can reccommend some sites for some of the other parts I mentioned if you're interested.