Polystyrene Bator First timer!.... What watt bulb???

I'm sorry but I do not know the answer to your query. However, I would point out that most of these new fangled bulbs do not give off heat so you would need to get some of the old type.

I'm sure someone will be along with the answer.

So I tried a 60 red bulb and was waaay to hot. I tried a 40w red bulb it was just over the temp needed. I tried a 25w normal bulb and it was only a small bit too low. I wondered if a 25w red bulb would be better but I want to get eggs in asap so I have invested in a reptile thermostat which will switch the bulb on and off when it reaches the correct temp. This I felt was the best option for the polybox incubator. I will use the 40w bulb with it.

So for others wanting to make their own incubator:

*Polystrene box with lid - fish transport box usually
*Clear plastic sheet - lid window for checking the chickies/eggs A takeaway box lid will do for this.
*Light bulb holder all connected ready to be plugged in (ebay - http://www.ebay.co.uk/itm/321096779649?var=510108471170&ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 ) this will be positioned on the inside wall of the poly box by cutting a hole and taped in place. Simples
* thermometer and hydrometer - usually something that'll do both. again ebay (  http://www.ebay.co.uk/itm/Digital-LCD-Thermometer-Hygrometer-Reptile-Incubator-Vivarium-1-5m-Long-Probe-/390575975245?pt=UK_Pet_Supplies_Reptiles_Spiders_Insects&hash=item5af0246b4d ) placed inside the box.
* pot or dish and a sponge. Yoghurt pot or similar will do and a sponge in it with water. This keeps the humidity and you add or remove as the thermo/hydro tells you. placed in the box too.
* A reptile thermostat. You will want the product which caters to a higher temp as I noticed most reptile thermostats only go up to 32C. The actual product is a Habistat Hi-range Dimming Thermostat. This can be ordered in most reptile websites, ebay or in my case Amazon.

I will get pics taken and uploaded.

I would say a poly box incubator is still the cheaper option because the other bits can be brought very cheaply. Poly boxes are usually free from a fish shop. Peep lid is a takeaway box lid (clear type) Buy a takeaway and you have a meal and a peep hole. Light bulb holder can be picked up in most diy stores very cheaply or use a desk lamp if its suitable. Bulbs are easy to get ideally a red one in 40w. The thermometer/hydrometer has to be purchased online from reptile shop or anywhere online. E-bay has very cheap ones. Pot and sponge... no explanation needed. The thermostat (as above).

Using these items you can make as small or as large a incubator as you want, so it will be the cheaper option. You will find it hard to find an incubator for less than £50 that can hold 20 eggs.

Spending so far:
Poly box -  free
Plastic peep lid - free (after the curry )
Bulb holder -  free if you have a suitable lamp already, if not £2.00 at macsalvors. look for the already wired one.
Red bulb 40w - £0.63p macsalvors
digital thermo/hydro - £2.99 on ebay
Pot - free could use the pot section of the takeaway box.
sponge - supermarket sponge are like £1.00 for 6
Thermostat - £39.82 this is the most expensive part. you could have a incubator box as big as a rabbit hutch and with adequate bulbs will maintain the heat for that size box so its worth its money!!

total spend - £44.44p
You won't find one for that amount  I will update on what hatches to see if it actually works

My incubator sounds similar to yours. We made a couple last year using the poly boxes. The incubators worked fine the main problem was fertility of the eggs.

I used a 40watt bulb, a pack of four can be bought from the pound shops. I put 2 holes in the incubator, one at the top right and one bottom left to me this provided like an inlet and exhaust and might help with your temps. The thermostat should do the rest of the hard work. We have tried 2 types from maplin and both have worked fine though the one with the digital display is more reliable. If you need part numbers let me know and i'll try to find them. You can make these incubators for under £20 if you use the cheaper thermostat from maplins which is £5.99 last time I looked. The viewing window on ours was from some old food packaging, just cut out and gaffa taped on. The bulb holders can be also had from the pound shop, the 99p shop does 2 holders in a pack and you can buy a extension lead from the pound shop and use the cable and plug. We used a 12v pc fan in the first incubator which are 99p from ebay delivered. The second one we made had no fan and worked better. The poly boxes can also be found for free in hospitals if you know any hospital workers. they use them to send blood samples from surgerys to hospitals.